PC-Dreamcast server...

I just got a new broadband connection last week, and so I was wondering if I could use the same connection for my Dreamcast, saving money for a seperate dial-up ISP. I found out that there is a way to set the actual PC as the server for Dreamcast, but the problem is that the broadband modem I use is connected to the PC via USB (http://www.ftel.co.uk/uk/products/consumer/fdx310.pdf), and there isn't any apparent way to connect it to the Dreamcast modem. So is there anyway I could work around this? Any help will be appreciated.
What? I have cable modem and no broadband adaptor for my DC. There's a way to run the internet through my computer from the cable modem to my DC? How is that done. I would like to try this out.
I have two network cards ethernet, i just bridged them together and was thinking. Is there a converter where i could just plug in my phone line from my DC into the other ethernet card? Would this work? Oh and sorry to ask questions in your post, but this just got me thinking