I'm working in a project and need to know how many PWM pins do I need to control speed and back / forward on a DC motor. The answer is 2 pins per motor? There's a way to use only one? I need to control 3 motors and only have 6 PWM pins
TX
Three PWM pins is enough for three motors but most motors draw more current than an Arduino pin can handle. Unless you are using very low current motors ( less than 40 milliamps) you will need some kind of external hardware. an H-Bridge is commonly used for controlling speed and direction. There are many tutorials for using motors with Arduino, have a look at some of the motor control articles in the playground: Arduino Playground - InterfacingWithHardware
If you need to ask for more advice it would help if you said a little more about your project and what kind of motors you are thinking of using.
Have fun!
This is the information I have about the motor.
Max amp draw 2.5. Use 5 amp fuse 12 V. I don't know if this is enough information but if you can tell me a bit more about how to connected to a PWM port would be great.
You will need an H bridge, to control both speed and direction.
Try to google "Arduino H bridge" this should give you lot's of info on just what you need.
Thanks for the advice. I found this tutorial and I was wondering if the TIP 120 is enough to handle the motor shown above.
http://itp.nyu.edu/physcomp/Tutorials/HighCurrentLoads
Like I said, I'm not a "electronic guy". Also I notice in this tutorial they use a potenciometer for the speed and direction. I also can control that from the arduino without the pot, right? To be more specific I can control the speed/direccion with a nunchuck.
Thanks
A TIP120 would work but would not allow change of direction. The last line of that tutorial says:
"A motor controlled like this can only be turned in one direction. To be able to reverse the direction of the motor, an H-bridge circuit is required. For more on controlling DC motors with H-bridges "
There is a link to an H-Bridge tutorial if you need it.
Thank you for your response mem,
What is a little confusing for me is, do I need to connect the TIP120 to the H bridge or the h bridge itself can deal with the motor requirements without extra components. Sorry to be so annoying but is my first arduino project 
You need an h-bridge that can handle the current of your motor.
Sparkfun has some that work on 2.5 amps or more:
http://www.sparkfun.com/commerce/advanced_search_result.php?keywords=h-bridge&search_section=products
and if you read through some of the robotics sites you can find more.