Get these things and use them (all free)
is where you can find most of this stuff.
Spybot Search and Destroy
Tweak Now Registry Cleaner
Kerio Personal Firewall (Blocks ads)
Go here and click download http://www.kerio.com/us/kpf_download.html
Run those weekly and stop using Internet Explorer all together.
Also run Disk Cleanup, Scan Disk, and Defragmenter every week.
All that stuff will keep your computer clean, free of crap, and running at optimum speed.
use AVG (Made by Grisoft) for a good virus software.