Well, I've got it.
Several roommates use my computer, and one of their friends sent him the virus. Obviously, my roommate had no idea what he was doing, regardless the virus is on it.
I don't have a virus screener. I found out after attempting to transfer a file from my Zip disk to a computer in the lab at school. That virus scanner did pick it up and informed me that the "Melissa" Virus was on the disk, which brings me to the conclusion that it's on my iMac as well.
I know an easy solution is getting a scanner and getting the downloads to get it off. However, I don't have the funds right now to do that. I've seen some free patches, but they're all for PCs.
Can anyone suggest a way I can fix this without getting a virus scanner/fixer?