An older Windows XP system can sometimes get into a state where complex software products do not install and uninstall properly. One thing to try when you have this situation is to make sure your XP system has the latest version of the Windows Installer. Microsoft has a KB article which describes the 4.5 version of the installer.

The downloads for various flavors of Windows can be obtained directly from Microsoft. Upgrading your Installer will ensure that you have the latest Microsoft fixes for the Installer component, and may possibly fix registry permission issues that are hampering some of your current attempts at installing third-party software packages.