I'm trying to get decent footage on youtube and in its help section on this it says the best format is mp4, divx. how do i export in divx, i see no mention of divx in the imovie sharing settings.
Well, the only thing I can think of is, while you're in iMovie, click on Share, and at the bottom, it should have a share... function (^- -S). Click on quicktime, and then expert settings. From there you can choose the format you save it as- i.e. mp4, or whatever). Like so:
You can also just output to DV stream (should be a giant file, but "lossless" quality) and then run it through pretty much any video compression package out there to get whatever video format you want.