Hi all,
Megveg - As mentioned above - free AVG virus scanner, version 7.5 is a smaller file than the latest if your worried about disk space/time etc.

Spyware blaster and Spybot are good/user friendly/free and work together to cover internet and your hard drive.
Spybot search and destroy will find auto dialers, adware etc and give you the options to remove. Take the snapshot of your system before running. Not all files are bad so always check the program owning the file before deleting.

Download the latest free versions from brothersoft.com

I'll assume you have a firewall program cause you wouldn't last long on the net without one.
Nick