I have had an tiger k8w myself for about a year and been happy.
2x240 cpu
1 Gb corsair (forget modsel sorry)
1x74gb raptor
1xmaxtor plus pata,1xhitachi 80 gb sata
I've used both nvidia ti4200 and 6600GT (see below)
However, I'm starting to suspect its chipset may not like the nvidia 6600GT, from what I have read the Thunder k8w using the same chipset does have issues with ATI cards. According to forums on
www.2cpu.com there is a problem with the AGP bridge in the AMD chipset used. YMMV
If I enable AGP (either NVidia or kernel built in) my monitor goes to sleep and I need to reboot. I have decided its not an interupt issue and I'm running the latest BIOS. It could be a driver issue but I've tried multriple versions. I did periodically get X freezes with my old ti4200 as many others have recently been reporting with othert chipsets and boards, but I am suspiciuos of this mobo/chipset.
Perhaps others here may be able to comment on the k8w 6600gt combination before you buy. I just wanted to pass along my experience. It is true however that others may have got it to work. The opteron is a nice chip.
Mark