Hi Jonathan.
I'm pretty sure that you're right about the receiver, almost any AM/ASK receiver at the right frequency should work as far as I know. I'm no expert though 
You might be right about the frequency, I've heard that the US X10 remotes operate at 315MHz, not sure about the Australian ones. The library should work regardless of the frequency though, since the protocol is the same. The timings might be different, but that's easy to adjust.
Please keep me posted on your progress, and tell me if I can be of any assistance. If you want to e-mail me, you can find my address in the license text of the X10 library source files at Google Code Archive - Long-term storage for Google Code Project Hosting..
Just checked out your site, wow! You might get some orders from me soon By the way: 315MHz receivers on breakout boards seem to be hard to find. If the US and Australian X10 is 315MHz, there has to be a lot of people searching for that. Maybe you could make a 315MHz receiver shield? 