K so some great thoughts going on here.
for motherboard switch to MSi K8n neo4-F, you do not need an SLI board...nor will u ever need an SLi board, waste of money, and no point in it. This motherboard is great, and when u wish to overclock, no mobo does it better, except for DFi Lanparty, but this still overclocks amazingly
Cpu, definitely get dual core. if u dont want to dish out a lot for a dual core. get an Opteron 165 or if u can a 170, and then overclock it like MAD! Opterons are the best overclocking processors, guys here get their 165 from 1.8Ghz to 2.8Ghz on air cooling, cool eh?
with that you'd want G.Skill or OCZ PC 4000 ddr 500 2x1gb dual channel ram to make it ezr to overclock without worrying about ram.
as for video card, i'd get the eVGA 7900 GT KO, seeing as how newegg has it cheaper than the other ones....or is that sale over?
for monitor, if u cant spend over $300 for an LCD, definitely get an CRT, it'll be in ur price range and great quality.