Compressing Video Files

I have a JVC video camera which only downloads into .moi files. I have since converted the files into .mov files using ffmpegx.
Now I have loaded the clips into iMovie but it can only seem to hold a maximum of 11 minutes of playtime for my DVD.
How can I get at least 30 minutes to an hour of playtime onto these DVD's?

I know that I should compress these video files but:
A) How?
B) Should I compress the clips when I convert from .moi to .mov? (How to do that)
C) Can I compress the recently converted .mov files and then should I load them into iMovie?