rtstine,
The best book I've ever read about futures is "The Futures Game: Who Wins, Who Loses, & Why" by Jones, Warwick and Teweles. It not only covers the basics of futures trading including the available markets, different types of orders you can place, picking a broker, etc., but also subjects like money management which becomes more critical with futures because of the higher leverage. This book was written prior to internet trading, so it won't give you much information about online execution, but the basics are still the same.
Another good book which does cover online trading is "The Complete Guide to Electronic Futures Trading: Everything You Need to Know to Start Trading Online" by Scott Slutsky.
One problem with futures, other than the electronic contracts like the S&P or Naz e-minis, is that there is still no direct access to most markets, meaning you're held hostage by floor traders and relatively slow executions, leading to greater slippage costs. My advice is to stay away from all but the largest, most liquid contracts like t-bonds or the S&P 500. Good Luck.
Kirk