UD.scr is necessary to run in 'Screensaver-only' mode. Otherwise it is not needed.

There are a few other files that go into the 'system32' folder aswell, which might cause you a problem.

However, you can try the following.

1) Open windows explorer and go to C:\Documents and Settings\***YOUR USER ACCOUNT***\Local Settings\Temp
2) Run WorldCommunityGridAgent.exe setup package.
3) After the 'Welcome' window pops up, look in the folder you opened in step 1, and you'll see a new folder. (Something like WZSE0.TMP but i believe it can vary.)
4) Copy this folder to your desktop and quit the installation.
5) Open the new folder on your desktop
6) Click Start > Run, Clear anything that maybe there in the textbox and type

msiexec /a

7) Drag the file UDagent.msi in to the run text box and click OK
8) Click next in the first window and in the second enter

C:\WCG\Program Files\WorldCommunityGrid\
(You can use any folder instead of WCG, BUT make sure you keep the \Program Files\WorldCommunityGrid\ bit at the end otherwise you'll end up with files everywhere )

9) Click Next, Next, Finish.
10) Go to C:\WCG\Program Files\WorldCommunityGrid and run UD.EXE

Just a word of warning, a number of companies won't be too happy if you do this without permission, so it maybe worth checking first.

Regards

Slug