Glad to hear that you're happy with your set. As for hooking it up to your mac, you have two choices: MIDI and audio. In either case, if you're looking at software too, it may be worth waiting a week to see how this GarageBand thing pans out. I was about to drop some money on an audio program, but I think I'll wait and see how it looks first- $29 is a lot better than $299.

Since you did get the Yamaha brain, I think you only need stereo inputs, which gives you plenty of options: USB, firewire, PCI, and then I suppose 1/8 audio input jack, depending on your Mac.