I downloaded Premiere Cs3 today, and while messing...

I downloaded Premiere Cs3 today, and while messing around I found that avi files don't mix well with it, but WMV are fine. What can I use to convert them? Hopefully it would be a free program and not a trial that lasts only the first five minutes of the video.

Off-topic: Like I said above I'm new to Premiere CS3 so if any one knows where I can get a manual, that would be great.