Ok, now I can see what sort of service you're on. You would probably have been given 4 options. CABLE, ADSL, WIRELESS or SATELLITE. As I see it the option you've settled for, namely WIRELESS, requires a special PCMCIA (or USB dongle) card. You are sending and receiving on different frequencies to conventional 802.11b/g WiFi (which is 2.4GHz). You are operating on Third Generation Mobile (cellphone) bands. This technology cannot be shared in the conventional manner that one would expect of an ADSL service. I would imagine you'd have to purchase another special 3G PCMCIA card, which could be an expensive way to get another PC on the Internet.
I would guess that the ease of use as regards wireless Internet possibly tempted you to go for this option. If you were to swap options and go for ADSL brought into the house on copper wires, then a conventional router, even a wireless router, could be employed.
This is my reading of the technology you have in Australia. However, someone with hands-on knowledge of the kind of equipment you're using may be able to offer alternatives...
Good luck.
ROGER - G0AOZ.