Booking with Jetstar.......select state?

Hi there, I'm just in the middle of trying to book flights with Jetstar airlines from Phuket to Sydney. I've filled out the whole form but when it comes to the address section it wants me to select state. There's no box for me to type a state in and no drop down menu either because my country is set as Ireland. However, when I try to click continue to go on to payment it wont let me. Keeps saying error: select state. Has anyone ever booked with them before and encountered the same problem? Any suggestions would be greatly appreciated, really want to get this booked and sorted........cheers