How much power will this setup need?

What GPU? The GPU could easily be the largest factor.

However, the 500w Enermax might suffice.
I know the 450w Corsair would be fine.
However, I don't know the Enermax off the top of my head.

DUH!!! sorry. 1x 8800gtx vanilla

thx for the reply

I have been advised that the amps on your 12V rails are more important than total watts.

get a good quality 650 or 700 watt PSU with at least 50 amps on the 12V rails. I have this system:
e6750
2 gig ram
asus striker extreme
xfi extreme gamer
2x 8800 gts 320 OC
2 hdd's
5 or more case fans
and of course the cpu fan, my PSU has 2 fans etc.
and my PSU:
silverstone s12 80+ 650 W is running it great: 52 amps on the 12V rails (or so they claim, i have not measured).

So go for quality and not quantity: I paid $180CDN for the PSU (almost a year ago).

Cheers.

if you buy a high quality PSU now then it will last for more than one rig (hopefully)