WhatThe 275 is quite a bit better than the 4870, even a GTX 260 is slightly better than the 4870. However you are right that it's a bad choice.
I wouldn't have thought that they use any more than a single 275... what are you planning on running it on?
Win7 needs to be 64-bit to use your 4GB of RAM effectively.
Spinpoint F1 - I would get the F3 for the small price difference as its quicker
izzop: Your spec looks good, but I really would get a retail OS over OEM as the OEM is basically a one-motherboard-only copy of windows.
May be look at this:
http://forums.overclockers.co.uk/showthread.php?t=18094652
Should be a bit cheaper than buying new.