I upgraded to 3.0 last night. After seeing your message I fired up my Apple modem and it works as advertised. I can access the internet in both OSX and Win XP at the same time.
Are you able to access the internet using the modem in OSX? Are you able to access the internet while in Windows using your broadband connection? If you are able to do both, you should be able to access the internet from within Windows using the Apple modem.
When you attempt to connect using the modem, are you unplugging your ethernet cable and disabling your wireless connection? If not, give that a try.
I have two network adapters setup:
Network Adapter 1; Bridged Ethernet
Network Adapter 2; Shared networking
Good luck!
Lew