here is an idea, do not kill yourself until they issue a patch...
look at the shear volume of posts about CIV 4 tech issues...
experience says your system is fine, wait.
not waiting means hours and hours of diagnostic hell imho.
the thought of CIV 4 being all graphics and sounds really puts a curve in the franchises history imho...
tell your brother to play CIV 3 until the patch comes out, else read the thousands of similar issues all with no single similar issues other than (1) crashing to desktop no matter the video card, bios driver, inf update, service pack, O/S version, retro driver installations, purchasing new hardware, etc.
a 6800 should rock any CIV game. 40 hours into a game until a crash sounds like nothing wrong with your PC but a programming error of some sort.
this old schooler is sitting back until the first couple of patches...
your question mirrors hundred of threads such as
http://forums.civfanatics.com/showthread.php?t=137685...
good luck, get your brothe a hooker and a couple spliffs cause the baby aint ready for prime time yet!