Need Suggestions On My Build

You DO want to overclock...right?

In that case, I would suggest different RAM, either of these kits will do fine:
G.SKILL 2GB (2 x 1GB) DDR2 800 (PC2 6400) $304.99
Team Xtreem 2 Gb Kit DDR2 (2x 1Gb) 4-4-4-10 800Mhz $305.00
Crucial Ballistix 2GB (2 x 1GB) DDR2 1000 (PC2 8000) $309.99

This will increase cost by about $75. However, you can easily save on the CPU and PSU without performance hits (with some effort, the E6300 will clock as good or better than the E6400)

CPU: E6300 $181.00 (saves $36)
PSU: 500W Silverstone (35A on the 12V rails ) $87.50 (saves $27.49)

The E6300 in combination with the P5B and good RAM will hit good clocks. You should be able to fairly easily hit 3.0GHz with RAM at 1:1. Possibly even better

Video card: SAPPHIRE 100189L Radeon X1900GT 256MB GDDR3 $134.99

I booted a vanilla P5B (second rig now) with my Crucial DDR2 1000 sticks (woops...forgot to recommend those in my previous post ), which are rated at 2.2V (a voltage not even supported by that board), but it booted without a hitch. The 2.2V is probably at DDR2 1000 speeds, but it likely still needs 2.1V at DDR2 800 speeds...

I would not expect an issue...

Did you check my suggestions above though? (and I didn't see a double post... I squeezed right inbetween)

Oh.. and do throw in a good aftermarket CPU cooler! An Arctic Freezer Pro 7 if on budget, or a Tuniq Tower (if you can find), Scythe Ninja or other high end cooler if you want to best.

Thanks! Good luck with both rigs