845 is dead so its out of the question
865 still major in the market with standards like ddr400 and agp 8x
915 big leap. newer technology is still nascent that is pci-e and ddr2
if u wanan go for it .. wait for sometime ... till they set in
my suggestion go for amd instead
ofcourse u have pcie in amd now as well with nforce 4
but ddr2 is still not supported
these newer technologies still have no extra added advantage over the current standards ... so it might not be worth going in for it yet
do post ur budget and the others will help u extensively !! trust me
and o yeah .. ull never repent an amd 64 rig