Hooking up MIDI keyboard to play in GarageBand.

I recently bought a USB 2.0 A/B cable to hook up my 2006 Yamaha Portable Grand DGX-220 keyboard to my Mac so I could play it in GarageBand. However, the computer doesn't seem to detect the keyboard. GarageBand preferences says "0 MIDI Inputs Detected." The keyboard's power cord is plugged in too. It came with a Software CD-ROM (USB-MIDI Driver), but it says it's only for Windows. Besides, I thought that it was only used to play the keyboard's instruments on the computer. However, I just want to use the keyboard as a "controller" to play GarageBand's instruments so I don't have to use Musical Typing anymore. Please help.