Simplest solution is purchasing a good recent anti-virus program like Norton 2009 or Kaspersky 2009, booting off the install CD, and using that to remove any virus material on the computer. Then, after the viruses are removed, get rid of whatever antivirus program was on the computer previously and install the newly-acquired software. The computer will probably run more quickly than it did (given that both scanners mentioned above are very fast and don't use very much system resources).