if you could note down that message and then let us know what it says, it will be allot easier to pin point the problem then
but as you think it is to do with your graphics card...
is your power supply powerful enough to take the new graphics card as they are quite powerful cards..what power supply have you got
did you uninstall the old drivers for your old graphics card before installing the new graphics card/drivers
have you got the lastest drivers for yuor graphics card..these all things to consider if you beleive the graphics card is the problem, but i am just guessing here as i havn't any information to go on!
the error message that points to the faulting device, will help i'm sure!
next time you get the error right down the whole error message, or in windows xp if you have it, there is an error log, which is in control panel,admin tools,event viewer