I've had a few questions regarding uninstalling Windows PowerShell 1.0 on XP to make way for PowerShell 20. It's actually quiet simple although not immediately obvious. PowerShell doesn't show up under Add/Remove programs as it's counted as a Windows update so follow these steps it you want to uninstall it.

1. Click Start -> Run
2. Type appwiz.cpl and press enter
3. Windows PowerShell will not show up in the list of programs as it is counted as a windows update, you must click the tick box "Show updates"
4. Scroll down and look for "Windows XP - Software Updates"
5. Underneath the Windows XP -Software updates entry is a list of all updates that have been applied to you machine scroll through the list and you will find an entry call "Windows PowerShell(TM) 1.0"
6. Click the "Remove" button to begin uninstalling PowerShell 1.0

You can find more details on this in the Microsoft knowledgebase at:  http://support.microsoft.com/kb/926139