If your using XP and a nvidea card
and experiance the well known lockup bug when trying to play games ect ect
the following should fix the problem,
1. go to display properties\advanced\troubleshoot tab\then un check enable write combining
2.go to start\run\regedit\the to the following key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management
create the following dword > LargePageMinimum set it to
ffffffff in the hexadecimal which will = 4294967295 in value -- reboot
3.try setting the agp apeture to 128MB loacated in bios settings
this will be a fix for many,