Hello, crdm--I'm still not clear on the legalities of copying commercial DVDs for any reason, so please proceed with caution, and do a little research on this matter first. Wouldn't want to get you in trouble!
First thing you'll have to do is extract the DVD content to your hard drive, minus the copy protections and region controls. The only program I know of for the mac that does this is Mac The Ripper: www.mactheripper.org. Yes, you will have compatibility issues with the region codes (US RC is 1, and I think Australia is either 3 or 4), but you can fix this in MTR. Try "0" first, then try it out on your DVD player (some players don't like it when the RC is "0").
Unless you're burning double-layer DVDs, you'll want to compress the resulting TS_Video folder to fit a standard single-layer DVD. The two out there that I know of are DVD2One and Roxio Popcorn (which is built into Toast, an awesome program to have if you ever burn anything else). Commercial DVDs are getting tougher and tougher to back up, so this may not always work. I've heard that DVD2One has more success with the tougher ones, but I don't think you can burn the disc withing DVD2One, whereas you can within Roxio. There's a third one out there that will do it all if you're using the DVD burner that came with your mac-- otherwise, it won't work at all.
One thing I've reverted to is to buy previously viewed DVDs with a lifetime warranty against damage (for like $7-10 at Hollywood Video), but this wouldn't resolve your region code problem...unless you bring a US DVD player with you to Australia maybe?