Lake Conroe, Lake Houston, and the San Jacinto river are the main places to ride in and around Houston.
You can't ride at M2's lake unless you're taking lessons or pay, and you have to live at Lakes of Katy to ride on their water as well.
Check out
www.gcwa.com for a local message board, and check out
www.har.com for a real estate website of just Houston based houses.
Good luck.