Do you want both computers on the internet? If so, you'll need to pick up a router (unless your DSL modem has more than 1 Ethernet port on it). If you need to get one, I'd recommend a Linksys 4 port router. They're very easy to configure and its a good quality router. If you want to go wireless, an AirPort Express ($99 USD) would work well in your environment.
If you're just plugging the DSL into your Mac, then it should be plug n use depending on how BellSouth does their DSL. All ISPs do things differently, but a lot of them are just plug it in, wait for the computer to get an IP address and then you're off and running. Mac OS X is pretty good and doing all of the above without too much trouble.