I have set up 2 ISPs and am running one now. First off you will need hardware, what do you have for servers, modems for dial in customers, are you planning on any wireless or DSL, ISDN? Can you have fiber brought to your location or are you planning on using copper T1's?
Do you have a good router, IDS, Firewall? What OS do you plan to use for your network? Answer some of these for us and this can be an interesting thread. I never thought of a tut for this... maybe I will start working on one.