That Intel chip is awsome, running a Q9550 and OC to 3.12 and is very stable. I would however go with a bit better board don't want to paint yourself into a corner with only 1 PCI-E slot.. this will allow you to expand if required. Looking at Newegg alone it does not have the best reviews, I personally own a Gforce 780i that has been bullet proof so far. The other thing I would replace is the HD, The WD Velociraptors are SATA II and have a larger capacity you could get 1 or 2 depending on your requirements and set up a raid array. With Raid 0 you could increase your speed incredibly but you lose your data if 1 drive fails. I do think though your 700w PS should be sufficiant.

Can I use any windows vista 64bit to see the 8gb of ram? - Vista will see all the ram, but when you go to install the OS ensure that you only have 2gig of ram in the machine MAX! Once the machine has the required update to prevent BSOD on loadup, you can add the other 6gig of ram you plan to put in there.