Holy hell, you running water cooling + 3 vid cards in SLI + 8 drives? That power supply is massive overkill.
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139006
I'd say 750W max for your setup, and that's still a bit much.
Video card, at your price point i'd go with:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814130468
Two of these in SLI would
greatly out perform that 4870. And it's in your budget since I just saved you $100 on your power supply, haha. If you'd rather go with one card vs two, a better choice would be:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814143190
Are you overclocking? The stock intel heatsink preforms reasonably well (and is free), so unless you're overclocking (or plan to) I'd skip the heatsink.
RAM is pretty cheap now, I say go with as much as you can afford.
I hope that windowsXP you plan on running is 64-bit, or else all that memory isn't going to do you jack shit.
I highly suggest installing the RC of windows 7. It's a great OS and it has that 'new computer' smell.
Which CPU? I see from a prior post that you linked to an i7. You can't run that on this board as it is a different socket. If you need a good CPU for that board I'd recommend a quad core Q9550
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115041
I assume you already have the hard drives, because the ones you posted are quite dated.
How does that Antec Three Hundred feel? Does it feel flimsy or look cheap? Was planning on building a PC this weekend for my nephew and was eye balling that case.
Edit: After seeing your case, you might be better off with a single card as you might have space issues.