What about Disc Copy with Toast?
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Insert the DVD, go to Disc Copy in Toast, press the Burn (red) button, wait til Toast says you to insert the blank DVD media and then do so.
Or you could rip the DVD using MacTheRipper for example and then make a Video_TS DVD in Toast by selecting Video_TS as a source.
Or you could use Disk Utility:
http://support.apple.com/kb/HT2059