What are the formats of the other movies (that you could move to iTunes)?

I don't use iTunes 8 (I use 7), but AFAIK 8 supports H.264, .mp4 & .mov files. So you'll need to convert your .avi files to a format compatible with iTunes. There are a few free converters around. I use 3GP converter.

Check out the threads below for more info & links. The second link has an alternative download link for 3GP if you want to try that.

How to transfer music to my iPod (& iTunes)

Itunes Problems