Interesting article on lifehacker on creating a slimmed down version of XP. I still can't decide if I want to try Vista on my P4 2.5 GHz box. It doesn't seem like it would be worth it and with hearing the good things about XP SP3 I'm guessing that's how I'll go.
http://lifehacker.com/374376/trim-down-windows-to-the-bare-essentials