Usually cable modems (Like NTL use) connect using either
USB or Ethernet
USB id=s available on Mac & PC but you will need MAC drivers for your modem.
Ethernet is a standard protocol that is supported by almost every computer, providing it has a LAN connection socket (this looks like a phone socket but slightly squarer with the clip in the centre) . No drivers are needed.
Using ethernet should work on the MAC. USB is less likely to work unless you can locate USB drivers.