A few weeks ago, I asked on here about what difference getting an upgraded HDD for a laptop would make. (it was being replaced under warranty), so I took the advice given, and paid a few pounds extra for the higher spec unit.
Initially the computer had Vista ultimate, but now it's been returned to me, I've installed XP pro, and the difference in performance is amazing. (I can't tell for sure if it's the XP, the new HDD or a combination of both).
It is now, without a doubt, the fastest computer I've ever used, with programs opening almost instantly.
I might consider going back to Vista sometime in the future, but it certainly won't be until they have released a couple of service packs to fix the numerous niggles with with it.