Also, most DVD's are dual-layer, using up to 8.5GBs of space.  DVD-R discs are all single layer and limited to 4.7 GBs.  If you have a dual-layer burner, make sure you're using dual-layer media.  If there's no copyright protection, or your burning software ignores it, it should burn fine.  Otherwise you'll need a DVD ripping application to trim the video down to 4.7GBs.