I normally use Compressor (which comes with Logic studio and Final Cut Studio) to help me produce content for DVD Studio Pro....
Did you click on "deinterlace video source" before exporting???
Are you based in America or Europe? I ask because that will change the setting you choose: NTSC is for America and Japan...
PAL is Europe.
OK. So, you've noticed there are a lot of different compression types ;-). Don't choose DVpal. That will output Standard Definition (SD).
As for size, if the video is definitely for DVD only then adjust it to fit to the DVD spec:
DVD's playback lower quality video - i.e. the size is 720x576 (PAL) and 720 x 480 (NTSC). DVD's also only playback mpeg-2 format.
Probably best to export without compression (None) - this will take up a lot of space!! For example, 1 hour HD footage can be as much as 350GB.
If I wasn't exporting for DVD I'd probably export to H.264. You can try this also, I forget it iDVD can import H.264 or not. I suspect it can...
you can drop your video file into iDVD which will then add it's own compression (mpeg2).
As for frame rates... I think 60 frames is unrealistic... did you shoot at 60frames?
Again, in Europe we use 25 fps (PAL) and in North America 29.97 fps (NTSC).
Sorry for this long post, but another question: Did you shoot in widescreen (16:9) or standard (4:3)?
I appreciate you may want to just choose the best compression and leave it to compress. But the above questions are very important and can help to find the best method for exporting your videos.
I'd also recommend checking out Compressor if you have it. Much easier IMHO... although it interfaces directly with Final Cut and not iMovie, it would still be very useful!