I'd have someone you know who is knowledgeable about desktops over to take a look at what that board will take and maybe walk you thru the selection and installation process...
There would be no reason to leave the old card in there.
Except in his case, where it is integrated
. Rather rockstar might need to disable the onboard video when installing a video card appropriate for his Motherboard.
yes, with Video cards rockstar, (ideally) you can generally just follow these steps:
1. Uninstall old video drivers.
2. Remove & replace old video card (if applicable, or just install new card)
3. reboot
4. run drivers from included CD. Afterward card should work with it's features. Could also run updated driver installer found on manufacturers web site.