My first robot(hopefully)

[programCurtis]

Recently I was bit with with the robotics bug. After a lot of Google searching and advice from kids on my high school's robotics team I decided that it sounded like a reasonable project for me to start. I'm still in the planning stages and I still don't know if will actually be able to t make this project work. Essentially I just want to make robot that I can experiment with. I'm on a very limited budget which complicate things even more. At the current moment I want to use and Arduino Mega 2560 as the controller. I want to use two

RS550 Motors - 12V from banebots along with two
P60 Gearboxes: Stock, Standard Shaft, RS-540/550 Mount, 16:1 also from banebots. From what little knowledge I have I understand that I'm going to need motor controllers for each of the motors. What I don't know is exactly what I'm looking for. I know that they will require a different power source then the arduino. So what do I use for motor controllers and what do I use to power them? I'm probably in way over my head, but I seriously can't stop thinking about this project and all the possibilities it has. Any advice is greatly appreciated.