I uninstalled SETI a long time ago, and have just reinstalled it.
In deference to BOINC's recommendation, I downloaded Virtual Box and Seti at the same time.
Now what?
Seti is running, but I can see no information regarding running SETI, or anything else, within it.
Additionally, BOINC's help page, where I went prior to composing this meassage, bears the title 'Live help via Skype or email', yet no email address is given.
It looks to me as if changes which have been made since I last visited BOINC/SETI have not been for the better - almost as if there is a wall of obstruction. It is now more difficult to get information.
I am quite willing to once more donate computer time to the project, but not at the expense of frustration if I have to fight the system.
It would (should) be useful if anyone who is connected to the adminstration team draws their attention to this post.
Meanwhile, if Virtual Box does afford any benefit to me, how do I run SETI in it?
Equal rights for equal responsibilities.
Equal opportunities for equal abilities.

VirtualBox w/BOINC is only recommended if you wish to run a project that requires VirtualBox. SETI@home is not one of them. As far as I know, Test4Theory is the only one that requires it because their Project Scientists have chosen to only release a Linux science app, and since most people run Windows, VirtualBox can be used to run Linux inside a virtual machine.
As far as getting information, all you need to do is ask on these forums. The one thing that has never changed since I started helping out in 2005 is the number of people willing to help someone with questions. That's why these forums were setup. They act as a user-to-user/self-help forum in a very community-related effort.

BOINC is the framework under which a lot of projects can easily reach out to hardware users to help them out.
Seti is merely one of those projects, although it may not use everything that's included in BOINC or the BOINC Installer.
As an example, projects like Rosetta@Home or Leiden Classical who do not have any GPU applications, don't have influence on which GPU flavor of the year is next supported by BOINC. They don't use it, but it's included in BOINC anyway.
So about the same with VirtualBox, which is a virtualization software that allows you to run operating systems such as Linux, Mac OS X, Windows XP, Windows Vista, Windows 7, Windows 8, Solaris, FreeBSD and OpenSolaris in a virtual environment inside the operating system that you run. So if you run Windows, you can at the same time run Linux, without the need to install this separately on part of a hard drive, and the need to reboot to switch between the OSes.
Some of the projects that run under BOINC use VirtualBox to run Scientific Linux that runs their science applications. Test4Theory is one, a couple alpha and beta projects are others. And because of a work-fetch problem that Test4Theory has with the (at this time) 'latest' versions of VirtualBox (4.2.18, 4.3.0 and 4.3.2), the included version is 4.2.16
It also speeds up things when you want to run Test4Theory, then you can now install BOINC and VirtualBox in one fell swoop, without you requiring to go separately to the Oracle website and getting lost on your way to install the correct VirtualBox version. It's efficiency.
Now, with that out of the way, you must have seen that the installer gives you the option to install VirtualBox. First it tells you it's a requirement, to then immediately tell you it's an option. You can opt-out for the moment to install VirtualBox. For at a project like Seti, you don't need it.
That's why there's also, still, the --just-- BOINC Installer. Also available from the same website, allows you to just install BOINC.
As for documentation about what it is and where to use it, you were right, there wasn't any anywhere yet. So I just edited the Release Notes, to take all that in: http://boinc.berkeley.edu/wiki/Release_Notes#BOINC_.2B_VirtualBox_installer.
I'll get the developers to look at the download page again, to see if we can change some more, make it easier to understand.

Thank you both for your replies.
Virtual Box has now joined the the big Recycle Bin in the sky.
Equal rights for equal responsibilities.
Equal opportunities for equal abilities.

Here Here! I couldn't agree more with each and everything you said. Frustrating and really lacking in clear instructions. SETI @ home used to be so easy. What happened. Now I'm being asked for donations at every turn. No!

Then why was VirtualBox automatically put on my desktop when all I wanted to do was start back up with Seti@home?

If you installed BOINC 7.2.28, and you downloaded the 90MB BOINC + VirtualBox installer package, then you would've seen these two screens prior to BOINC being installed:
This window in the installer will tell you that VirtualBox is required to be installed, however, once you click Install, you'll get:
Which shows it's optional. Clicking NO here, will not install VirtualBox and only install BOINC.
It's a simple thing of reading the windows as they come up on your screen, and not blindly click Install and Yes without reading any of the information given to you. As then you'll end up with 'VirtualBox automatically put on your desktop'.
The Release Notes that you can click to go to from the Download Page will now show a lot more information about BOINC + VirtualBox, including on which projects it is needed and why BOINC development has chosen for this method of co-op installer.
The VirtualBox page in the same Wiki has a lot more information, which will probably be added to over the coming weeks. (don't look at me, I'm done writing the documentation without information from the developers.)

Here Here! I couldn't agree more with each and everything you said. Frustrating and really lacking in clear instructions. SETI @ home used to be so easy. What happened. Now I'm being asked for donations at every turn. No!

Don't confuse Seti with BOINC. Seti@home is STILL easy. And as far as donations go, they send one, maybe two, request emails annually, certainly not at every turn.

Then why was VirtualBox automatically put on my desktop when all I wanted to do was start back up with Seti@home?

Because you didn't pay attention to the installer. VirtualBox is an OPTION, not an automatic install. Didn't you read Ageless's post above, where he said:

Now, with that out of the way, you must have seen that the installer gives you the option to install VirtualBox. You can opt-out for the moment to install VirtualBox. For at a project like Seti, you don't need it.
That's why there's also, still, the --just-- BOINC Installer. Also available from the same website, allows you to just install BOINC.

Then why was VirtualBox automatically put on my desktop when all I wanted to do was start back up with Seti@home?

Because you downloaded BOINC w/VirtualBox instead of plain old BOINC? Why did you download BOINC+VirtualBox and not the other 'standard' BOINC that is also the recommended version? You had a choice in which to download.

I've downloaded the latest version of Boinc with virtualbox but have no idea what I should do with it! I run Seti, Primegrid, ABC and Asteroids on my PC, Some advice would be appreciated please.

Hi Pauline - the answer to your question was right here in this very thread! ;-) See Ageless's post for more information.
tl;dr You don't need VirtualBox for the projects you are running.

Thanks, I did see Ageless's post and have now uninstalled virtualbox - I followed instllation instructions but somehow managed to miss the list of 4 projects it is needed for! :-)