"Piggy-backing on the launch of LRO will be the Lunar CRater Observation and Sensing Satellite (LCROSS), which is designed to watch as the launch vehicle's Centaur upper stage strikes a permanently shadowed region near the south pole of the Moon. NASA expects the impact velocity will be over 9,000 km/h. It is hoped that spectral analysis of the resulting impact plume will help to confirm preliminary findings by the Clementine and Lunar Prospector missions which hinted that there may be water ice in the permanently shadowed regions. LCROSS will fly through the debris plume, then approximately 4 minutes after the Centaur impact will itself crash into a different part of the crater."
http://en.wikipedia.org/wiki/Lunar_Reconnaissance_Orbiter

LCROSS won't be hitting the moon at a low orbit lunar velocity [which is around 2 km/sec] instead it loop behind the Moon and hit the Moon at velocity similar as though coming from Earth/Moon L-2- which is about 2.5 km/sec (9000 kph/5589 mph). LRO will arrive at the Lunar orbit and then it will take something like a month before LCROSS loops around before impacting.

LCROSS will go into a highly elliptical lunar orbit, though I see no mention of it, it would be exploring the "fuzzy boundaries"