First things first go to monster.com or any of the other job sites with informational articles and find the obligatory "interview questions" article or post. I know they are out there... Need to know the "general" questions first. Why are you leaving last company, top strengenths and weaknesses, bla bla bla... they are all kinda the same.
Next find out who will be interviewing you. If its a manager, hit the non specific stuff, OSI model, network topology, general security, TCP/IP stuff anyone could ask and answer if given the information before hand.. Because thats what most managers do, read questions off a list.
If you are going to be interviewed by a technical person, or a manager and a tech, hit the specific stuff harder. Find out what kind of gear they use, become farmiliar with the different models, if they use cisco, know that cisco has 2500, 2600, 2800, 7200 routers... you don't need to know everything about each of them, but basic knowledge can take you pretty far. Beyond that knowing what they use can be HUGE.. Even if you don't know a thing about it, showing intrest in a technology they use will win you points. I know this first hand.
Lastly.. if you are uber serious about it, and you have some time before hand. Get someone you know to do the interview first. A technical professional, possible a dummy resume, send them in and get them to write down or remember everything "important" they ask. Have them ask pointed questions.. what technology are you using? What are you going to be using? Anything that might give you the edge beyond what other candidates might know.
