The 2008 Tecumseh Trail Marathon is sold out but consider joining the Yellowwood Lake Fun Run (just over 5 miles) - it is a great sampling of what Tecumseh course and venue is like, if you are considering Tecumseh for a future year.
www.DINOseries.com/marathon
It starts at 11 am at Yellowwood State Forest, between Bloomington and Nashville.
If you are ambitious and adventurous, you can run the Yellowwood Lake Fun Run then drive over to Nashville (less than 10 minute drive) and run the Brown County YMCA Reindeer Romp 8k, which starts at 1 pm! (See Indy Runners Race Calendar for info)