Here are a few distinctions...
Emerging: The most current forms of methodology "emerging" in any/all church denominations.
Emergent: More theological/philosophical movement...an actual structured organization with identified leaders.
Here's a quick quote:
"Through time people started even saying 'Emergent Church' instead of 'Emerging Church' or use both terms as describing the same thing - instead of having Emergents focus more on theology and Emerging Church more on methodology as it started initially. [From Part Two]"
Here's part one, and part two.
[HT: Justin Taylor]