If you are going to do a fair amount of dirt trail riding, you might want to consider a hybrid with a bit more of a mountain bike personality. Such as a Gary Fisher Kai-Tai. I've seen them selling in the mid-$500's.
http://www.fisherbikes.com/bikes/bik...rt&bike=Kaitai
Or for a bit more, the Specialized CrossTrail:
http://www.specialized.com/bc/SBCBkModel.jsp?spid=21925
Although the hybrids I listed earlier can certainly handle bumpy trails.