When installing the Visual Studio 2005 May Community Technology Preview, there are three key things to remember:
(1) Everything from the VS 2005 March CTP must be uninstalled before starting: MSDN, J#, .Net and VS.
(2) You cannot install the VS 2005 May CTP from DVD. I don't know why, but you have to copy it to a hard disk on your PC or somewhere on your LAN.
(3) After the May CTP .Net Framework has installed it will ask you to restart. Once the machine has restarted, the setup will run automatically but it will fail. You need to manually restart the setup process after this and it will continue on perfectly.
I don't know what the difference is between a hard disk and a DVD install. Maybe it is because of an error in my download of the ISO image. I wrote two DVD's and both exhibit this strange behaviour. If you have experienced this same behaviour, I'd love to hear from you so I can know whether or not this is a recurring problem.