Is the conference in the hotel as well, or downtown?
There are two greenways which connect relatively close to the Gaylord
(google for "shelby bottoms greenway" and "stones river greenway"-don't be confused by the other stones river greenway in murfreesboro). The Shelby is a ride into downtown after crossing the newly-completed pedestrian bridge over the Cumberland
Some of the local shops will lease bikes, although I'm not sure exactly who. Check with Cumberland Transit, Jolly Cyclist/Bike Pedlar, Nashville Bicycle or Eastside Cycles- all should be easily google-able.