You need a Wireless ADSL router, i.e. with built in ADSL modem. All of the "free" modems supplied by ISPs are USB and will not work with a Wireless Broadband Router. Doesn't look like the one Richard posted will work without an Ethernet ADSL modem attached (and I am guessing in the states this plugs into the ethernet port of a Cable modem )
Myself I like to install either the Linksys ADSL Wireless G or the Netgear DG834G as they are easy to setup and configure.
Networking a Mac to this setup shouldn't be too difficult. I managed to talk my sister through (over the telephone)networking her boyfriends Mac to her PC to share the internet connection over the telephone, and I know nothing about Macs, and they no nothing about computers
The numbers (DNS / IP / gateway) are all the same whatever computer you use.