A Reply from another Post was
I just thought I would take the time to update everyone on my situation.
Nothing I did to correct/fix registry permissions worked for me. Consequently, I resorted to reloading the disk image for my laptop (i.e. reinstall Vista and all drivers). I then loaded all of the known recommended updates for Vista from MS Update site.
I tried to install Expression Studio 2.0 (only selected Media, Web and Encoder) again and this time it choked on loading .Net Framework 3.5. Given that a failure now occurred with a freshly installed Vista, I think the existance of an installation error cannot be blamed on me.
I solved the problem by downloading the standalone .Net Framework 3.5 installation file from MS Downloads site. The standalone file installed without any problem and allowed Media, Web and Encoder 2.0 to install without any problems.
May be this helps you a little bit