Programs your computer should never be run without.
Anti-Virus (Free download AVG , Avast, etc. Lots of Free downloads. Commercial stuff is <$25 a year)
Spybot Search and Destroy (finds and destroys spybots and other nasty stuff. Allows you to set an interface that will not allow registry changes without your permission. Free download)
Adaware (another type of search and destroy. Free download)
Cleanup (Kills everything in ALL your temp folders. If I run this first Spybot and Adaware dont ever find anything to kill. Free download)
Hijack This (A registry key killer. Will enable you to remove ANYTHING from ANY registry on your computer. Free download)
Firewall (Limits what can be installed across the net to your computer. Should come as part of your Operating System unless you run something other than Windows)
If you dont have most or all of these on your computer and you get online..... you are asking to get smacked.
It might be wise to also consider running your operating system on one hard drive and put all your other stuff on another. Then if you have to wipe and start all over... just erase the OS drive and plug n play the other afterwards. No lost data.
Just some things to consider.
Later,
KayBay