martin, id recommend you vista 64 over xp64, it already has better driver support and its getting better by the day.

i dont understand why you should be limited when ocing the fsb when using 8gb, you will be limited by mem speed though. 1000 should be possible with tweaking and good mem, maybe even 1100 but anything above that needs damn good memory and a damn good board.
And tony is right, getting 8gb to run can be tricky on some boards, even at stock speeds.