I have never worked with iDVD but with DVD Studio Pro I’ve found that exporting as a Quicktime Movie and clicking the “Same As Source” button works great (don’t use the Avid DV Codec). However, originally capturing your Avid footage at either mixed resolutions or at DV 25 411 often causes issues. You can do a video mixdown of your whole sequence to 2:1 OMF and then export it if you’ve captured as described above.
Good Luck,
Will Meyer
Sure Shot Productions, Inc.