Installing anti-virus on a infected system is not a good idea. It most likely get infected during install and becomes worthless. I suggest you run 2 (3?) online scanners to remove at least the majority of the viruses you have before installing anything. Instead of a online scanner you can also get the BART cd (there is a trial which fully works). Get it on a clean system, create the cd and put it in your system. Boot from the cd and scan the whole system.