This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
The answer to your first two questions are "yes". There is a single Thread object for each thread.
"Live" Thread objects always belong to a ThreadGroup, which keeps references to them. Therefore, a runnable Thread can never be garbage collected. They become eligible for collection after they are stopped.