The reporters over at the terrific First Read offer this preview of how things will play out tonight:
The caucuses will be called to order at 7:30 pm ET (6:30 pm local time) on the Democratic side, and they begin at 8:00 pm ET (7:00 pm local time) on the GOP side. Democratic candidates have to hit a 15% threshold of support in each precinct caucus to win delegate equivalents, and supporters of candidates who don’t attain viability can realign with other candidates. By comparison, there is not a second-choice aspect on the GOP side; the Republican results are simply a “straw vote” of everyone who attends. Anyone can caucus in either party: A participant simply has to prove residency and register to vote in that party that night. So independents can caucus on either side, and Republicans can re-register as Democrats that night and caucus, and vice versa. The turnout on the Dem side could be anywhere from 125,000 (what it was in 2004) to 150,000-160,000 (and perhaps even higher). Since two of the major GOP candidates -- Giuliani and McCain -- aren’t spending a ton of resources in the state, Republican turnout is likely to be lower than the Democrats; figures being tossed around are 60,000 to 80,000.