it seems you want to really push the processor!
At those sorts of speeds i am sure you would need water cooling, or you will hit the maximum speeds from the teameratures you reach rather than the components themselves. Personally I have no experience with water cooling.
- The case has a few liquid cooling features so possibly you had thought of that already.

Trying to find a "quiet" 10k rpm HDD
If you go with that thermaltake case and use all the standard case fans and count the fan on the graphics card you will be looking at about 100dBA already. I wouldnt worry about the HD noise it will sort of be drowned out!
But i would recommend definatley going SATA, the speed increase still amazes me when copying larger files between my 2 Sata drives and 1 IDE drive.

For the benefits of XP64 i dont think that amout extra is worth it. Its personal choice but as its not main-stream yet (and doesnt have too many purpose built 64 bit products) I dont think it would be worth the money.