RAM - Two sticks of G.SKILL DDR2 800, CAS 4-4-4-12, 1GB each
CPU Cooler - ARCTIC COOLING Freezer 7 Pro
Also throw in 2 DVD Combo Drives and 2 SATA drives. No overclocking on the RAM or GPUs. Assume whatever the worst case scenario would be in terms of power draw for everything.
Also, if the extra power draw from the Q6600 being overclocked is a lot and won't bring much extra performance, then I may just not do it.
Edit - I just use the Extreme PSU Calculator, putting in 85% TDP, 20% aging, 2 SATA HDDs, 2 DVD Combo drives, 1 80 cm fan, 1 120 cm fan, 1 240 cm fan, 5 USB devices and the rest of the stuff put here, including the overclocked Q6600. I came up with 649 W.