Hell, I'm still trying to figure out why I can't just rip one DVD to another.
Unless I am misunderstanding what you are saying...
I use Nero on a Windows XP Pro box to smoke my DVDs to copy media that I actually play. It's a fairly slow burn, but it works well. BTW, you'll need several gigs of free disk space to do it.
My IMAC doesn't have DVD burning capabilities, so if that is your issue, I am unable to suggest anything.