get server to work through cable modem?

I used to have a t1 line with 4 ip addresses
Now I just have a cable modem with 1 ip.
Is there a way I can get to my sever from the internet using the cable modem?
I have a domain name that I want to point to the cable modem IP and have it go to the server
I am running windows 2k server and IIS 5
any ideas?