One of my favorite Microsoft applications is the often used but officially unsupported Tweak UI utility. I discovered some of the registry tips that I've provided over the years by looking at registry changes after I used Tweak UI and finding other items that I could modify in a similar way.
Microsoft is aware of Tweak UI's popularity and made sure that the Windows XP version was available when XP launched last week. Tweak UI is part of the Microsoft PowerToys for Windows XP, a 939KB download that includes 11 utility extensions for XP.
My favorite feature in this generation of PowerToys is the "Open Command Window Here" addition to system folder context menus that the PowerToys installer adds. This task item lets you launch a command prompt (cmd.exe) in the context of the current folder. I often use the command prompt, and I often want to be in a specific folder. Given how complex paths with descriptive folder names can become, the ability to navigate to a folder by using Explorer and to launch a command prompt in that folder context is a significant time saver for me.
The Resize Pictures PowerToy adds a resize option to the context menu when you click an image. This resize feature is what XP's built-in image-resizing option (the Send Pictures via Email dialog that you get when you use the "E-mail this file option" from the File and Folder Tasks menu) should have been in the first place. The tool lets you custom-size an image or resize the original without creating a copy.
The nine other tools included in the PowerToys download let you add interesting features and applications to your XP system. The tools are of varying utility, and you might not use them all, but they're worth checking out.