Yep. Cable modems usually bridge a real public IP to the first device to come up on the LAN side.
Most don't require PPPoE, like SBC does.
Put a SOHO router behind the cable modem (ie; Linksys) use DDNS to resolve the changing IP on the WAN side, and point either port 80 or 591 to the private IP address of the machine hosting the FM.
You can use any available port, but 80 and 591 are considered "standard".
Make sure that whatever port you use, that FM IWP is set to the same port (Advanced button in IWP sharing setup)
Most cable modems aren't too smart, so after making address changes within the LAN, you have to reboot the cable modem to recognize the new addresses.
If you don't want to buy a little router (<$100), then make sure that you have and configure a personal software firewall on the PC/Mac. Then open the desired port here.
I know this all sounds like Greek to a non-network person, but I tried to use as much English as possible.