Basically with Emergent/Emerging, it's a movement started by arrogant men (and women) who are not only "liberal" in their theology (i.e. non-Christian philosophy posing as Christian truth), but they basically seek to redefine and reinvent the faith altogether for the "post-modern generation"--hence, the Emergent or Emerging Church.
There is a slight different between the two, but both are awful.
Emergent: It's almost like what Unitarian Universalism would look like if "Christianity" were the dominant religion they emphasized. For instance, they might call themselves Christians, while incorporating Buddhist elements, Oprahisms, and really bad poetry. They deny essential doctrine: Penal Substitutionary Atonement, faith in Christ alone, the Trinity, etc. Oh, and don't forget the Socialist politics. (McLaren, Bell, Jones, Tickle)
Emerging: Churches that seek to make Christianity "more relevant" to modern culture. Looks a lot like the Seeker Sensitive Movement, but more extreme. They're generally not as liberal as the Emergents, but it's still bad.
The movement has infected all denominations, with the exception of more conservative ones. For instance, the only Presbyterians I think who could be infected would be the liberal churches (such as the PCUSA)