So many ways to answer those questions!

Firstly, you can run the UD WCG agent in the background and still use another (more pretty) screensaver. The trick is to avoid screensavers that use excessive CPU. I do not advise running the agent in screensaver-only mode because some of the current projects have infrequent checkpoints and it would be all too easy for the agent to get in a cycle where it never reaches the next checkpoint, and makes no progress at all.

But if you want to just run the screensaver for some good reason (if the computers are used for real-time or CPU intensive tasks, for example) then you can force the screensaver choice using Group Policy. All aspects of the Windows desktop can be locked down in this way, but it's an easy way of preventing your users from disabling the WCG screensaver. Ask if you need help with this.

My recommendation is to use BOINC and not to restrict the screensaver. Indeed, don't use the BOINC screensaver at all - let the users chose whatever ugly abomination they wish. Install BOINC as a service, and it will run in the background even when nobody is logged on. You can monitor all your computers using BOINC View. Again, you will need pointing in the right direction on this - it's less trivial than it should be.

If you want to advertise your participation in WCG, then perhaps set your login wallpaper to one of the WCG wallpapers provided by Graham. See his post in the Chat Room forum. That should compensate for the lack of WCG screensaver.

All Group Policy templates are is an easy and safe way of setting registry keys (GP can do more, but the registry is all that concerns us here). XP Home doesn't support GP, but the registry settings are there.

These are the relevant settings:

Hide screen saver tab
KEY: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System
DWORD: NoDispScrSavPage = 1
Screen saver
KEY: HKEY_CURRENT_USER\Software\Policies\Microsoft\Windows\Control Panel\Desktop
STRING: ScreenSaverActive = 0 or 1
0 disables screensaver altogether
1 enables screensaver specified in SCRNSAVE.EXE
Screen saver executable name
KEY: HKEY_CURRENT_USER\Software\Policies\Microsoft\Windows\Control Panel\Desktop
STRING: SCRNSAVE.EXE = path of the screensaver
Password protect the screen saver
KEY: HKEY_CURRENT_USER\Software\Policies\Microsoft\Windows\Control Panel\Desktop
STRING: ScreenSaverIsSecure = 1
Screen saver timeout
KEY: HKEY_CURRENT_USER\Software\Policies\Microsoft\Windows\Control Panel\Desktop
STRING: ScreenSaveTimeOut = value in seconds

In addition to changing these values (and hiding the screen saver tab completely) you can prevent your users tampering with the settings by changing the permissions in the registry. Be careful!

I cannot guarantee the accuracy or safety of this information. Use at your own risk and take all normal precautions.