Well there is no point running 4gb until you get 64bit windows (as has already been said). Windows 32bit will only recognise it as 3.25(I seem to remember, its been a while since I had 32bit). So I'd stick to 2x1gb sticks, just make sure you get the fastest speed possible. Or get 64bit windows and go the whole hog of 4gb, you WILL notice the difference, especially if your using vista...