ah, yeah, I'm using windows. I got the cable to hook my psp up to the tv to watch videos and stuff, so I plan on watching these on tv.I've used xvid4psp with great success.
http://www.winnydows.com/news.php
Of course, this assumes you are using a Windows PC.
PSP video 9 is another option.
http://www.pspvideo9.com/
Because I don't want to pay for anythingWhy does it have to be free? Well, you could try Super or Video 9
http://www.pspvideo9.com/