After weeks to trying to remove a Trojan virus from my computer, I was told that I could reset to the factory operating system to get rid of it. I realize I will lose all of my prgrams, but I don't care any more. How do I do this?

Yep it's a simple case of boot to the recovery CD's and follow the on-screen instructions.

But save your data first! Burn to a CD or DVD or USB key.

On an HP, during the boot process is a choice to enter Recovery. You can use that (if you don't have a Recovery CD) and run the Recovery utility.