Another bit of advice, since you're going to be bashing a stadium truck at high speeds and are a new driver, be SURE to get a harcase LiPo. If these things get damaged ie: punctured, torn etc... they CAN catch fire and are difficult to put out. A hardcase LiPo will protect you from this.
http://www.hobbypartz.com/77p-sl5000...-hardcase.html
Also, make sure you go to the Duratrax website and get a measurement of the battery compartment and whether or not the 3S will fit. Don't worry, if it doesn't then you can buy an inexpensive velcro battery strap or use zip ties. Just make sure that it stays in there tight. Even though it's protected by the hard case, you still don't want it flopping around.
You're also going to need to replace the battery connector on the ESC with either banana plugs (that come with the batteries) or replace both with either Traxxas or Dean's connectors (I like Traxxas better). For this you'll need the plugs and a soldering iron. Don't get a RadioShack crap one.
http://www3.towerhobbies.com/cgi-bin...&I=LXL362&P=ML
Find some place local to get your banana plugs (hardware store, electronics store etc) or order from Tower or go to a local hobby shop if you decide to with Traxxas.
Get a soldering pen/gun at a local hardware store as well. Don't get anything under 60W.
If you decide to go with banana plugs. Be extra, extra, EXTRA careful to NEVER EVER plug them in backwards (red to black, black to red) VERY BAD, very hot, very burny/melty things will happen. A Traxxas or Deans connector will not allow you to plug them in backwards. I don't want to see your new toy end up a puddle of smelly plastic and rubber.