What do I do if a TV show I want is not available on iTunes?

OK, so I want this show that I like called Ghost Hunters on my iPod, but they don't offer it on iTunes. I use Ares to download some of my music, and I can get some episodes off of there, but I don't know what to look for. I'd have to convert it from AVI to what exactly? And should I look for a certain screen resolution for it to fit on my 3G Nano? Or is there any where else I could download it for free?