From Microsoft website:

PowerToys add fun and functionality to the Windows experience. What are they? PowerToys are additional programs that developers work on after a product has been released.

Note: We take great care to ensure that PowerToys work as they should, but they are not part of Windows and are not supported by Microsoft. For this reason, Microsoft Technical Support is unable to answer questions about PowerToys. PowerToys are for Windows XP only and will not work with Windows Vista.

Recommended tools:

RAW Image Thumbnailer and Viewer - Allows you to edit RAW format files right from windows explorer!

HTML Slide Show Wizard - This wizard helps you create an HTML slide show of your digital pictures, ready to place on your Web site.

Alt-Tab Replacement - With this PowerToy, in addition to seeing the icon of the application window you are switching to, you will also see a preview of the page. This helps particularly when multiple sessions of an application are open. This cool function is already built-in in Windows Vista.

Image Resizer -This PowerToy enables you to resize one or many image files with a right-click. If you are using Windows Vista, you can download Image Resizer Clone.

Virtual Desktop Manager - Manage up to four desktops from the Windows taskbar with this PowerToy. Similar function as the desktop manager for Linux!

Check out the website for more cool add-ons for Windows XP.

Microsoft PowerToys for Windows XP