black viper is a classic.
For xp it is impossible to beat boldfortune.net, but yuou really gotta want to do this... there are over 400 pages of info.
For win7 32 or 64, this site covers a lot of the basics that apply to anyone:
Speed Up Windows 7 - Ultimate Guide To Make Windows 7 Blazing Fast!!!
I've done these mods to my win7 64 bit machine, including the registry tweaks, and so far so good. Not using it for audio, though.