The current Win32 installation was built using Microsoft Visual C++ 2003 (Version 9). Therefore they need the Microsoft .NET package to start. If you don't have .NET, you will only get a quite unspecific error message that the application failed to start, and reinstalling may fix that ... but (shame on Microsoft) there is no clue that a missing .NET framework is the reason. Unspecific error messages are useless.
I am not sure which .NET version is required. Windows XP users may need both version 1.1 and 2.0 already for several different programs, most probably one of them will be the right one for PS too...