A few things to try based on your OS being XP.
1...Disconnect from the net...disable Firewall and Anti Virus...Remove screensaver... reboot then reinstall.
Re-enable Firewall and Anti Virus.
If that hasn't worked try 2.
2...Go to "RUN" command
Type in MSCONFIG
Go to STARTUP tab
Look at your startup programs to see if you have any of the following listed!...If you do...and they have a check mark in the box...uncheck it.
PDVD SERV
PCM SERVICE
POWER DVD
DVD LAUNCHER
EHTRAY
Reboot and go back to screensavers...see if that has worked.
If not then try 3.
3...Go to here to Kellys Korner.
http://www.kellys-korner-xp.com/xp_tweaks.htm
On the left number 51...download and use tweak...it's a lot safer then messing about with the registry it'self.
Other then that the only thing i can think of at the moment is a conflict if you are using a wireless mouse or keyboard...MS has a patch that will fix the problem.