Install iPhone SDK 3.2 Beta 5 saperately

I was told that in order to keep my original XCode and iPhone SDK environment clean, I should install the beta SDK, like iPhone SDK 3.2 beta 5, separately. I tried twice but they both failed, stuck at the screen saying "Prepare for Installation ...".

Eventually I found a great way to solve the problem: reboot. After rebooted, I could install the beta SDK in a new DeveloperBeta folder. Problem solved!