If the cleaners don't work, try removing the Skype program entries using the program install/uninstall troubleshooter from Microsoft. It can be found here: http://support.microsoft.com/mats/progr … _uninstall
I run malwarebytes free virus removal software (if you download it, do NOT accept the free trial of the live antivirus protection software. It will become annoying when the trial is over). Malwarebytes is the only thing that seems able to remove many viruses that often have to be hand removed from the registry. Everytime I've had to help someone, my research usually brings me to malwarebytes. I would make sure Skype is then fully uninstalled. Do all microsoft updates available, make sure you reboot your system one last time and then try downloading a fresh version of the Skype installer and attempt the install again.
Chances are you can skip the virus check. It sounds like there's some old files floating around in the registry messing things up and the microsoft tool should fix it if Zurf and Beamer's cCleaner suggestion doesn't do the trick.