Questions from a newbie regarding persistant viruses

I am new to computers but learning fast. I am using widows vista. I am also usig XP. It seems lie I have had seven stubborn virues that cannot be removed. They are backdoor.bot and trojan.zlob. There are seven of these viruses that are affixed to my music, video, and picture files which I have not even used. Like I say I am a newbie and i just got my computer a week ago. I run the malwatre scan on quick scan and the long scan (this is one of the best malware scanners in computerdom) and I keep seeing the same viruses. I keep removing them and then I run the scan and there they are. I decided to reformat my hard drive twice. I finish reformatting run scan and there they are again. Someone told me the viruses are on my copy of xp or vista but not likely vista and he told me to get a new copy of XP or vista. Here is where I show my ignorance. How do I get a new copy of vista or a new copy of xp? I had vista and xp preinstled when I got my computer. I don't even know what a "copy" of vista or xp is. Is it a CD you can buy? Is it available for dowload if you pay for it? Recently I came up with the idea that I could destroy these viruses by wiping my hard drive with a wiper utility. The ulility is said the destroy the whole operating system. Does this mean I will need to buy or download a new copy of xp and vista after the hard drive is wiped? I hate getting viruses and I have a cheesy firewall that came complimentary along with a cheesy virus protection service. Can you buy a firewall machine of some kind, a hard ware firewall as opposed to a software firewall that you plug into your computer and would do a superior job of keeping your computer from being infected? There is a guy in my college class who is smitten with me, a computer geek, who keeps mailing me and I am afraid of viruses because he keeps sending me pictures and weird encoding in his mails. Would anyone care to meditate of my problems?