The X1900GT is a bad choice for the price. The 7900GS is cheaper and will overclock to speeds faster than an X1950PRO.
The x1900GT used to be a good choice when it was 150 and the 7900GS was 180...now its just not worth it.
I would go with an E4300, the Cheapest DDR2-800 G.Skill ram, and a DS3 for high overclocks.
I own an E6300 but the E4300 has been known to be able to hit 4.0ghz with cheaper ram and it's about 15 cheaper as well.
The Arctic Freezer Pro 7 is an awesome cooler for the price but make sure you do not get ripped off by like newegg by paying $69.99 for one, It should be somewhere 25-30 bucks.
E6300 w/ Arctic Freezer Pro 7 @ 3.6ghz 1.4Vcore
Antec 900 Case
EVGA 750i FTW Mobo
4x1GB of G.skill DDR2-800
2 8800GT in SLI
22" Samsung Syncmaster
1 250GB WD and 1 Seagate 7200.10 in RAID 0
Corsair 520HX 3DMark06 Score: 13900