Wanna help me upgrade my pc?

so my friend is selling me his graphics card, so i figure i might as well upgrade the core parts of the computer while i'm at it. my budget is around $300. this is for a modest gaming computer upgrade. i'm not hardcore, just wanna run games like assassin's creed, bioshock, and left 4 dead pretty well.

i need:

Harddrive
CPU+Mobo 2.5ghz atleast preferred, i hear intel+gigabyte are good brands
DDR2 Ram
Powersupply


my current specs for my custom built rig are:

graphics cart: nvidia Geforce 7600gt (upgrading to an 8800gt)
CPU: AMD Athlon 64 3700+ single core 2.2 ghz
Mobo: Asus A8N-E
Memory: Corsair 1x2 1gig DDR RAM (new mobo will be for DDR2, though)
Hard Drive: WDC WD800JD 80 gigs

newegg DID have some deals, but i waited too long and now everything is super expensive again. i don't really know where to look, so i was hoping you guys could help me out! what's the best i could do with the amount of money i'm willing to spend?

Tri core AMD 710 + Asrock 780g mobo mATX $163
http://www.newegg.com/Product/Comb [...] mbo.212282

2x2gb DDR2-800 Corsair ram $35 amir
http://www.newegg.com/Product/Prod [...] 6820145241

Western Digital Caviar SE WD3200AAJS 320GB $49 (thanks outlander)
http://www.newegg.com/Product/Prod [...] 6822136098

Corsair 450 PSU $55 amir
http://www.newegg.com/Product/Prod [...] 6817139003

Total: $302

I agree, Intel E5200 would be a good one. I've seen it for like $90 CDN. Intel P43 or maybe even P45 motherboatds are about $100, again that would be CDN. I just got a new Gigabyte EP45-UD3R. Antec Eatherwatts 500W is quite good, Accually, execpt for the the motherboard, I would say all of the stuff ewood has said is very good.