XPfree is now a guide for XP, Vista and Win 7. I find people charging for system optimisation and trouble-shooting information on the Internet (musicxp.net, experts-exchange) embarrassing.
People charging for that stuff have garnered that information from other people on the web and real life who have - in the majority of cases - given it to them for free. A long time ago I put together a guide for optimising XP systems for optimal performance, and recently I've updated it to cover Vista and Windows 7. So, regardless of whether you're "free of XP" or just wanting XP information for free (yeah, cheesy I know - I just can't be bothered changing the URL), here is your info.
A bit about me: I program, have a BSc in Comp Sci & build/troubleshoot computers on the side. So I have some idea of what I'm talking about. I also run a small but interesting music studio in New Zealand, which, as you may know, is somewhere near the penguins.
Hopefully this guide helps you :)
Matt.
Additional optimisation tips - Extra detailed information for tweakheads.