There's some amazing stuff to hit up in that area, but you'll need some rain for sure.
The only shop in the area worth checking out for gear and rentals is Suncook River Kayak, just outside of Concord (probably 30-45 min. from durham. The owner, Kerry, is super cool and will usually hook up demos for free if your buying somthing.
If your out there and there happens to be some rain/runoff going on, I'd recomend hitting up the follwing (most within 1 hour of durham):
The North Branch of the Pemmigewaset (sp?) in NH - IV to V
Wells River in VT - IV
The Contoocook in NH - III-IV
North Branch of the Contoocook in NH - IV to V
Warner in NH - IV
The Sawyer in NH - V
The Swift in NH - IV
CrackPipeWave in NH - manchvegas park-and-play
If there aren't any flows, maybe you'll catch some swells over on the NH/ME coast.
Also, you can track down other boaters in the area on NPMB.com.