The best bet is to make an image of your hard drive and make incremental backups onto an external hard drive. This way you can always revert back to a state of PERFECT. I use “Acronis True Image Home” and can honestly say it saved my and my familys butt numerous times. Although we all use an antivirus program, sometimes things get through. To restore an infected PC back to a state of perfect takes about 20 min. This is by far the best software investment I have ever made.
On a side-note. It is wise to password protect your passwords in firefox & IE. My son just had to reimage his hardrive to prevent any more security leaks in his browser. Seems that he picked up some sort of virus that pulled out and sent all his passwords to an ip address in Nigeria, resulting in a mass funding transfer parade. Cost him thousands. PASSWORD PROTECT YOUR PASSWORDS.