Unable to install dotnetfx 3

I just downloaded dotnetfx and whenever i try to install it I get an error


Install latest version of Windows Installer and then try again.

I installed windows installer but it didn't solved the prob.

The prob. Is that I can't even install wmp 11 and visual c++ 2005

Your windows is currupt, sometimes this happens to me too, i then simply reinstall xp, & the problems are solved.

As for the .NET Framework, just yesterday i had installed .net framework 3.5 on my friend's pc, & it works fine.