DART will launch this afternoon. Spacecraft and it's Pegasus booster will be dropped from an L1011 carrier aircraft after takeoff from Vandenberg.
DART will demonstrate autonomous (sp?) rendezvous technologies.
I didn't catch the launch window times, but NASA TV coverage is scheduled from Noon - 2PM EDT. For those of you outside of the US that's about 40 minutes from now.
NASA TV schedule: http://www.nasa.gov/multimedia/nasatv/MM_NTV_Breaking.html
Streaming NASA TV:
edit: corrected for daylight time
[Edited 2005-04-15 17:23:19]