Posted on 
Sep 16, 2010 03:22 pm Hi man, and welcome to HRC.
Actually with a lot of newer controllers and gear, midi data is actually sent via USB. My Xboard controller is also powered off the USB port on my computer. So you should be able to connect the kit directly to your Mac via USB, and control the kits that way.
While I don't have a full fledged studio (I will someday though, money willing!) I can say that I was also looking at the Alesis DM10 kit as a possible future addition. Looks like it's gotten some pretty good reviews too. The Roland kits are also worth a look.
Anyway, that sorta setup should do you well. Install the software for the kit, and run the USB from the module to the computer. Open your DAW, check the audio/midi settings, and make sure your drumkit is enabled. Then, load a VST in your DAW (i.e. superior, BFD, Jamstix, etc.) You may need to map the VST sounds to the correct drum head. But once that's done you should also be able to save that mapping for future use I think.
There will probably be some configuring and calibration of the drum kit to suit your play style as well. Basically, how hard you hit the drum head is sent over the wire to the computer, and registered as velocity data.
If for whatever reason, you decide you do want an external audio interface that has midi, I'd suggest looking at the Presonus, Echo, TC Electronics, RME, M-Audio, and MOTU interfaces. Some of those can be had for pretty good prices. MOTU and RME might cost you a kidney depending though, but their midi-only interfaces are pretty reasonably priced. :)
Midi data sent from the kit is recorded as a midi track in the DAW. Certain hits or sounds will be mapped to a certain key or midi note. (i.e C4, D4, E4, etc.) The loaded VST will "play" the midi data, and output as the audio for whatever instrument or patch the VST is using.
Many kits come with pre-generated grooves (for those of us who aren't top-notch drummers) and some are capable of composing their own grooves on the fly, like Jamstix, which is what I use. Might not be much use for a drummer, but listening might give some ideas or inspiration.
Hopefully that helps, and I hope I wasn't too confusing or anything.