I'm going to pass on the i7 then.
I don't plan to overclock anytime soon so should I stick with DDR2 or DDR3?
ASUS M4A78-E AM2+/AM3 AMD 790GX HDMI ATX AMD Motherboard supports DDR2 1066.
This is great overclocking ram, 800 is fine:
Newegg.com - G.SKILL PI Black 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model F2-6400CL4D-4GBPI-B - Desktop Memory