Oh wow, where to start with this one. Hmmm, well, there is a lot of reading that goes along with this, and I'm not sure if you're a collector or casual reader, if your just a casual reader I would suggest picking up the various trade paperbacks of the crossovers, probably a lot easier to track down.
http://comicnews.info/?p=45 Generally there is two giant stories going on in the Marvel Universe, one comprising the mainstream heroes like Cap'n A, Iron Man, SpiderMan etc etc and one comprising the Mutants, Xmen those guys. To understand the Civil War story line and what's going on you need the Avengers Dissembled arc and maybe the House of M limited Series if you have the money, it ties up Avengers Dissembled, but doesn't really have much to do with the Civil War. If secret war, although referenced in the story line, has any major tie in to Civil War I'm yet to read it or they haven't revealed it. The Civil War seems to be followed up by the story line just starting now in Secret Invasion which is running through the Avengers books. FYI, to understand what's going on, you don't need Civil War:Frontline, it's just a series about the heroes fighting told from the perspective of a couple of journalists, I read it, but it didn't really add to my understanding of the civil war reasons.
Something else you might want to check out that just wrapped up is Planet Hulk/World War Hulk story line. Planet Hulk is Hulk issues 92-103 I think it was, followed by World War Hulk. Pretty good stuff.
I've been collecting for about 25 years, so I can try and help you out with most of it, although to be honest, a lot of the tie ins for these series if I don't already collect the book, I won't pick up the tie in. It's just a marketing scam in my eyes.
