XPize is a resources transformation pack for Windows XP and above. It replaces most of the non-XP icons, AVIs and BMPs that Microsoft has always overlooked. The installer simply automates the process of replacing resources in critical system files, making your XPs look better. It also includes some extras and an updater which you can use after visiting Windows Update.
Requires Microsoft .NET Framework. (Note that .NET Framework is included in Windows XP. It is recommended to update to the latest version.)