If you already installed Windows PowerShell v1 and you try to install Windows PowerShell v2, the installer will tell you that the previous version has to be removed first. Your first thought would be to go to "Programs and Features" to remove it, but you won't find it there. From "Programs and Features" click on "Turn Windows features on or off" and uncheck "Windows PowerShell" from the window that pops up and then click "OK". Now you should be able to install Windows PowerShell v2 CTP.
This one took me a little time to figure out and I know it stumped at least one other person, so I thought I'd share.