Of course the cable does not use windows DHCP. What you have to do is get a DSL/Cable router that will sit on the users network. That router will automatically get the cable providers dynamic IP address and you are free to use any IP addresses you want inside your network. Almost all DSL/cable routers will also do DHCP which will work with a windows machine. For Example

INTERNET
|
|
Cable Modem
|
|
DSL/Cable Router
(has 2 IP's one assigned by the ISP,
and the other a private subnet)
|
|
INTERNAL LAN
(Uses DHCP address assigned by the router)


By using this scenario, you will be able to use a single NIC and leave DHCP enabled on it so it will grab the proper network settings whether at home or at work.