If Comcast if your provider, AOL is only a top-level application. You won't have an IP through them, but one through comcast. Previous, AOL used to dial up to its servers, connect you, and give you an IP. Now, it merely sits on top of your existing connection, giving you all the options AOL previously had, but using Comcast's speed and service.
Unles you have a dialup line and a cable line going in to your computer (both modem and network card installed and in use), you'll have to just use the comcast IP. If you do infact have AOL connected (as in you dialed their server, and connected) you can use the bind ip located in options dialog (alt+o) connect->localinfo and I think it's the IP field. I've never bound an IP, as I've never had more than one network interface I've needed to worry about. If anyone else is positive, or I'm wrong, please let me know.
Again, unless you have cable working, AND you dialed up to aol, you will only be able to use your comcast ip.