I use Toast 7 Titanium from Roxio.
If you were to use iDVD, I guess you'd need to use iMovie to convert the video files before sending to iDVD to burn. I haven't done it this way before. I have opened up the odd file in iMovie however. There are other mac options. But not for free.

You need to downld the video in avi or mpeg. Then let your burner program convert it if it has the abiity. BTW there might be other alternatives for converting. Mpeg Streamclip (free) is a possibility.

But without all the mucking around & testing & trials. Toast is normally the way to go for Mac. See if you can get it. Toast 7 is best!