This allows you to use different Radiants without having to load new projects all the time.
Just copy the radiant.exe file over your old one (if you haven't got it on the CD the back up). Then execute the .reg file and you're done.

This works by changing the registry entry that KPRad addresses. It uses software/KPRadiant instead of QERadiant. The only down side is that you'll have my colour and window settings.
By Oggie Kovatchev