If you're second display is not detected in the Windows XP Display Properties Settings, even after a system restart, then try going into the Nvidia Display Settings.
There should be a tab which says something like Displays, on the left in the menu tree. You should then be able to activate your second monitor from there.
If you're still having problems, then try checking the My connected TV is not being detected
in the Troubleshooting tab. If you have the newest Nvidia Display Drivers installed, then the similar checkbox will be located in a different tab.
If you still can't find success...post back!