Go for Acer. It's 2 Hour servicing is good. I feel that XP is more stable. Vista is still pretty new and there may be some compatibility issues with some websites, especially if you do Internet Banking.
I have issues with acer's plastic body and general build quality... Go for one with at least 1gb of ram, 80gb of HD space and a decent screen. Most laptops have pretty bad LCD's (low contrast/colour saturation). And yes stick to XP for now.
geta macbook. for PC notebook, id go for ibm thinkpad. not the sexiest looking notebooks, but they get the job done and have been very reliable for me.
i would stick with XP... frankly, the only reason to switch to vista right now for me would be for D10 games, which arent really even out. and really, you wont be playing those on ur notebook in any event. vista which just suck more resources from your system in any event.