Error in Vista platform while running any program

I’m using Vista platform and about two days ago I started getting this error every time I tried to run a program, except for MSWord and Windows Messenger.
C:WindowsSystem32Version.dll is either not designed to run on Windows or it contains an error.
I cannot even install an Anti-Virus Programs which many forums I read suggest, because I get the error message right before the Setup Wizard starts. I am totally lost and would greatly appreciate any help.
