paul lets face facts here, I know a few folks who use comcast and dont have problems, you are trying to set up an fserve (for what reason I dont know). And you havent even got the router sorted out yet! Please follow some advice, instead of trying to run (fserve) learn to walk first. Setting up a linksys router is as easy as falling asleep, you dont need the handbook or any cd it is all there in the options even a help file is included (depending on the model of your router).
Anyhow forget anything to do with comcast go to http://192.168.1.1
(using your browser) It will then ask you for a username and password. Unless you have alterd these they will be the default. (NEVER ever give out these to anyone) and basically thats it all the help etc etc will be there all you need to know is what ports to forward (see portforward.com for more info)