dsl and opening and closing ports with routers

[Brent Harding]

					If I get dsl some day, how do most routers deal with whether or not to
allow a certain port? Do they have files like a traditional linux system?
What controls their ip address, is it jumpers on the back that there's 4
sets of numbers 1 to 9 that you turn on and off to give it the ip address?
How is the password usually set at default, when one of these are
installed, when you get dsl? I'm sure that nonstandard ports are probably
blocked by default (speakfreely, shoutcast, netmeeting, and many other
non-standardized protocols), someone told me somewhere most have a config
mechanism to open and close ports to certain hosts.