Fresh UI is a kind of tweaker's heaven: With it you can change scores of settings in XP, many of which you no doubt never even knew existed. Want to alter most any aspect of the Windows interface? Go ahead. Customize the Start menu? No problem. Change global menu settings, the way applications work, and dozens of network and Internet settings? You can do all those things, and a whole lot more.
Note: This link takes you to the vendor's site, where you can download the latest version of the software.