Loveletter is one of the more common virii found on KaZaA and other file sharing progams. I have also ran into CIH (which was an infected crack), Sub7 server masqurading as a keygen, and Kriz.

Back when I was repairing boxes, loveletter was acting as an MP3 file with .vbs appened to it, such as song.mp3.vbs. The best way to avoid these problems are to use the latest virus virus definitions, do not download files from file sharing apps or look at the file sizes... file sizes are usually a dead give away. That why it is so important to not to download anything under a meg (such as a keygens or cracks) because they are the ideal size for virii or trojans.

Hope this helps