Adding to Ian's post:
Make markers in your timeline by pressing M. Then press M while the playhead is over the marker to access the details. Click on the Add Chapter Marker button and <CHAPTER> will appear in the "Comment" field.
Do not alter this code in any way. If you want to name the chapter, change the "Name", not "Comment".
Then go to Ian's instructions (Export - QuickTime Movie, not Export - Using QuickTime Conversion) and the resulting movie file will carry chapter markers when imported into either DVDSP or iDVD, and also when converted into m2vs by Compressor.
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