Just to add....if you use a router connected to your modem rather than connecting your mac straight to your modem, the mac "problem" (as the ISPs see it) disappears. You just network your mac normally to the router. No "is there a mac driver for this modem?" problems. No mac support required.
There are other advantages (this applies to Windows machines too):
1) A usb modem uses the computer's processor to help it along. Your performace is degraded by plugging it straight into your computer.
2) You can have as many machines as you like all connecting through your router. This gets around, say, the NTL problem where you have to register the MAC address of each device connecting to the box, and you're limited to two addresses. You just register the MAC address of the router and that's it.
3) You can have wireless internet access if you either use a router that has a built-in wireless basestation, or you attach a separate basestation to your network.
4) Only one firewall is required on the router, it covers every computer on your network.
5) As all your machines are networked together, you can have a networked printer that you can print to from any of your machines. And file sharing between your machines is easy.
Wireless/modem/firewall/router/switch all-in-one costs around £100 (eg. D-Link - personal experience of this very easy to set up)
Or you can do it for free if you have an old, unused PC (say a Pentium 75): I use a linux router based around IPCop (
www.ipcop.org) - you don't need to be a computer geek to install/use IPCop, it's really easy. I've attached a rescued/repaired Apple Airport Basestation (puffy capacitor problem - capacitors replaced..works like new!) to the network so that the laptops can connect wirelessly. Total cost in money £5 for the replacement capacitors, £25 for a little switch. I appreciate though, that this kind of thing isn't everyone's bag! If so I do recommend the all-in-one things as mentioned above.
Alcina