Notes:
Used eBuyer because I know my way around their site and because they are usually cheap. Feel free to look at other sites to see if you can save a few £'s here and there.
Parts:
Vista Home Premium x64 OEM - What you want.
Samsung F1 - One of the fastest drives on the market. 1TB.
Sony DVD Drive - Cheap drive, Sony (quiet), retail, comes with a copy of Nero.
Q6600 - Great CPU. Can be overclocked to 3.2-3.6 GHz with air cooling. Better than any AMD CPU on the market.
Corsair 650w - Good price for a good amount of power - not modular but a very good make and a good performer.
Z-5500 - You wanted them.
OCZ RAM - Was going to get a cheap branded DDR800 kit, but 4GB of Crucial memory was £58, £67 for much faster RAM seemed like a good idea. Choesen because cheap for spec.
X-Fi Xtreme Music - Proper X-Fi, good card. If music is really important an Auzentech X-Fi card or Asus Xonar card may be a better idea.
Gigabyte board - Cheap P45 board, has dual 16x lanes for crossfire. No RAID but overclocks pretty well.
4870 - Faaaaaaaaaaaaaaaaaaaaaaaast. Can buy another for crossfire if needed.
Antec 900 - Cases are a personal thing, but some to check out are the Antec 900/1200, Stacker 832, P180 (/P182) etc. Antec 900 is a good case at a reasonable price.
Arctic Silver - thermal paste (goes between CPU & heatsink) - one of the best on the market and very useful.
Freezer 7 Pro - Cooler for CPU, will make it cooler and quieter and look cooler. Akasa 965 is known to be slightly better but couldn't find it.