You should download ccleaner and defraggler.
http://www.piriform.com/ccleanerhttp://www.piriform.com/defragglerI have used them for years.
I also use spybot, Avast Anti-Virus, and highly recommend Commodo as a firewall.
Best of all, it's all free...I've used all of the above since '04 and I've never had an issue and I'm on the internet allot.
Ccleaner is like an enema for your computer and all the temporary files and crap that gets stuck on it. It's also got a great start up tool so you can get rid of allot of useless crap that starts up and just use it when you actually want. The registry cleaner is good to.