Carlos,
Not sure about renting, I have no exp there. I do know that the Hill Country has some excellent riding opportunities. Do a google search for Texas Hill Country rides. At the local shops, there is plenty of ride information. Fredericksberg(burg?) is a nice touristy German Town, ask the locals which restaurant is the most authentic. Most of the smaller towns have nice town squares with the old court house in the middle. there are a few caverns to see, can't think of any other natural sites. Towards San Antonio, coming form the North, New Braunfels (sp?) is nice(another German populated area). Head towards the river(tubing area, signs everywhere) fun place to hang out for the day. Shiner Texas, home of Shiner Bock beer, is a nice place to visit. They put on a Bocktober fest with many live bands....a tour of their brewery is possible.
Have fun and enjoy