Do I need to use a motor shield to activate a 12 VDC linear actuator?

Do I need to use a motor shield to activate 2 12VDC linear actuators or can I just plug them into the arduino duemilinova? I am new to arduino so Im not really experienced with this. The actuator uses a DC motor and is created by Firgelli Auto

Here is the link for the actuator... http://www.firgelliauto.com/product_info.php?cPath=69&products_id=248

Also, how would i rig this up when using an external power source?

Don't cross post please.

Link you provided says the motor can draw up to 10 A, so you can't power it directly from Arduino. Your options are either a motor shield which can provide that current for both actuators at the same time, an off the shelf motor driver, or a custom built H bridge.

It seems that it is a voltage device, ie, if you apply 12VDC it will react. But since it draws a lot of current, you will definitely need a power MOSFET to actuate it. Make sure your power supply can supply enough current it draws, otherwise you will have an unstable system.