More or less what V7 said. A few things though:
(1) I don't believe the kidnappings that sparked off 2006 were a calculated provocation. The reason is simple: Tsahal soldiers aren't easy to kidnap. You can't just go "Ya Hussein, go get me a couple of Tsahal grunts, willya? I'm getting bored here, we need some entertainment." (In fact, the opposite story -- that the kidnappings were orchestrated by the Israeli side as a casus belli for an attack prepared in advance with American cooperation -- at least has the advantage of being physically possible. I don't believe it went quite that way either, but that's going off on a bit of a tangent.)
(2) The Lebanese government does not have the means to disarm Hezbollah. The Lebanese army is reasonably well-trained and pretty disciplined, but compared to the battle-hardened Hezbollah veterans they might as well be toting peashooters. Moreover, it consists of Lebanese with dual loyalties -- to their community and to the army. That means that in any serious confrontation between the two, the Lebanese army will (a) lose on the battlefield and (b) split.
(3) Hezbollah does not have the means to impose its will on the country either. It has the unconditional support of at least a plurality of the Lebanese Shi'ites, who are the biggest ethnic group in the country, but very little leverage with anyone else. That essentially means that they're unassailable in their strongholds, but can't do much (other than make mayhem) outside of them.
(4) No, the country can't be physically divided along sectarian lines. The geography won't work -- it's a mosaic with most areas actually mixed; there are reasonably "pure" enclaves (the Maronite heartland, the Chouf, Ba'albek, a slice along the Israeli border), but the coastal strip where most of the people live is mixed, and the mountains consist of villages with different dominant sects living next to each other. (This is one reason Lebanese civil wars get so bloody -- the belligerents start out within shooting, or even rock-throwing, distance of each other.)
So, the ultimate causes for the conflict lie in the make-up of the country, various historical injustices and grudges, and a long, sad history of foreign interference. (In this case, Bashar al-Assad's famous threat to Rafic Hariri, shortly before his assassination, of "smashing Lebanon over his head" springs to mind.)
(5) The proximate cause for the conflict is the power struggle over the presidency and the next government. They had pretty much agreed who would be president, but they hadn't managed to agree about the government, and the conditions under which it works. Specifically, Hezbollah wants a veto over any cabinet decisions, while Sa'ad Hariri's Sunni Future movement and its allies doesn't want to give it. So we have a country with a continuing standoff, no president, and tensions building ever higher. Add to this the fall of the dollar (the Lebanese pound is pegged to it) and resulting price inflation, the economic fallout caused by the instability, and general frustration, and you have a pretty explosive mix. Think of it as a pool of gasoline (the ultimate causes) evaporating in the sun (the proximate ones); all it takes is one spark to make a very big boom.
(6) The immediate cause of the conflict is the governments rock-stupid decision to dismantle Hezbollah's private telecom network. This is obviously one of Hezbollah's most important strategic assets (it's what gave them effective command and control over the 2006 summer war), so they're not about to just go "OK then, go right ahead." (It's rock-stupid because, as stated above in (2), the Lebanese government doesn't have the means to go mano a mano with Hezbollah; therefore, this was about as smart as throwing rocks at a bunch of Hell's Angels. But then if the Lebanese were smart about politics, they wouldn't be in this mess in the first place, would they now?)
Edit: (7) I don't see any external military interventions happening at this time either. Israel certainly doesn't have much stomach to go a second round against Hezbollah; Syria has nothing against the country going up in flames (their long-term plan _could_ be that after a couple of years of fighting and couple of hundred thousand dead, they can ride in again to rescue the country from itself... and re-establish dominance there.) The Americans are, um, busy, and their last trip to Beirut wasn't much fun anyway (although they might send in a battleship to parade along the coast and maybe shell a few goats, y'know, as a "show of force"), the French are too smart to get embroiled in this mess... and, well, that's about it.
