Controlling DC motors

Hey I was wondering how could you hook up a power source and program one of these things to go backwards and forwards and possibly give half speed?
24 Volt Electric Scooter and Bicycle Motors - ElectricScooterParts.com one of the 24 volt 100 watt motors

more info, i have the Arduino uno and I am willing to purchase the Arduino motor shield
Thanks

Hmm, 100W means 4A at nominal load, bit too powerful for most Arduino shields I think - you need to measure the winding resistance to calculate the max current at stall (that could be up to 50A!!), then you’ll need a decently capable MOSFET H-bridge motor controller that can handle those peak currents.

Also if you are running from 24V batteries select a 30V or higher controller, not 24V as charging batteries brings them up to 28V easily…

Something like the beefier controllers here perhaps:
http://www.pololu.com/catalog/category/94 but many other suppliers exist.

ok I'm following you for most of it. With the other beefier controller that you brought up, do those just control a single motor? I'm trying to make something that can use differential steering to drive. Any ideas?

You'll have to look around, there will be dual motor controllers too I'm sure - single controllers are more common. Did you measure the stall-current (ie winding resistance) of your motor then? Or locate a datasheet?