When you say "the only thing", you do realise that is enough to make PC folk laugh out loud. I suppose you didn't turn it off to install it either ? TURN OFF MCAFEE (If you can. Some versions can only be disabled by uninstalling it). With that (or the dreaded Norton) running, it will be slow anyway. Get a good free AV (
AVG Free - Download antivirus and antispyware software for Windows XP and Vista) and stop polluting your computer with rubbish. And when installing / uninstalling, turn it off. Job Done.