I downloaded last version of viclient and I cant run it on windows xp. The Log shows:
2010-07-15 15:12:25.296 Log for vSphere Client Launcher, pid=3300, version=4.0.0, build=build-208111, option=release
2010-07-15 15:12:35.984 A fatal unhandled error occured in vi client
2010-07-15 15:12:36.046 System.AccessViolationException: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
see if this helps
It not helps, I have installed all new updates of net framework 2.5.