Hi snowdonx, welcome to xda-dev.
I don't see why it wouldn't work in Australia - but I can't say for sure so someone else will have to give you a definitive answer there.
As far as making your own ROMs - everything you need to know can be learned here. I'd suggest reading some of the newer guides in the Hermes forum to get started.
To give you a head start - there's a couple basic things to be aware of. First, newer devices like the Hermes and Treo 750 will not allow flashing of custom ROMs, or more correctly, ROMs that aren't signed with a carrier or manufacturer certificate. The bootloader (SPL) enforces this. So the first step in getting custom ROMs on a device is putting in place a modified bootloader that allows unsinged ROMs. The number of folks who can do this is very limited compared to the number of folks who can build customer ROMs.
Creating the ROMs, in a nutshell, involves dumping an existing ROM using tools available here, making modifications, rebuilding the ROM, and flashing.
Hope you enjoy your stay here. =)
Originally Posted by snowdonx
I have a few questions in regards to the Treo 750 WM6 rom
Will the AT&T rom work within Australia?
If no why not?
What skillsets are required to make your own rom?
I sincerely thank you for any help.