I would like to clock up my computer security and heal some files that have been corrupted

by a bad ass virus and I want to finish with Trojans, spywares, and adwares once and for all. I'm pretty much a newbie and I need help!

First of all, how do you restore your computer??? I believe the virus I ate (I forgot it's name) corrupted some of my system files...Whenever I click properties on my desktop, an error messege comes up saying there is a problem rundll32.exe...

Second, my MSN LAGS like hell...Typing messeges isn't a problem but when I hit enter, it takes like 5 seconds for the messege to go on the screen and send it to the person I'm talking to. MSN games don't work and the voice chatting doesn't work

Third, buttons (not pictures, the round dot things in the middle) do not appear

Fourth, (anybody play Warcraft 3 or Starcraft Battle.net here) When I host a game, nobody can join because of my Wireless ADSL Router settings (I don't have a firewall) How do you change these settings so they can join?!

Fifth, anybody recommend me a good firewall(free)??? Or another anti-spyware or any recommendations on security???