I missed this thread. I have a Roland TD6-XK.
There's a few things to consider when getting an electronic kit:
* Metronome - it should have this as a minimum!
* sound of the drums themselves in the module (the sound rather than the number of kits)
* stable stand!
* trigger zones per surface - for pads and cymbals
* chokable cymbals - can you mute them by holding them.
* audio out for headphones
* midi out - see note later
* audio mix in - for playing along with your favourite tunes on the headphones.
* kits available
Also check:
* if you get a bass drum pedal (usually you don't)
* drum throne as usually you don't.
I'd go with closed back headphones and any small amp will not give enough bass.
Now onto the fun part - MIDI.
It's worth noting that if your drumkit has MIDI you can use it to trigger a MIDI software package to create the sound so the drum sound isn't as important if you have MIDI out on the 'brain'.
It's worth it's weight in gold in my opinion.
My TD6 has a good range of kits for my needs but even TD20 players often use VST Sample libraries with sounds that have been created and packaged professionally. The result is that you can have a sound better than a TD20 with a kit far cheaper.
A midi-usb cable is reasonably cheap and you should have a look around at software for your computer (I use OSX so I don't know what's out there for windows/vista, sorry).
The lack of features such as choke, rim or single-zone pads will limit what you can do but in reality if you've not played the drums before it's going to be a while before you get to that.
I have to say I've not heard of "Session Pro" but I have heard of the DM5. It looks like out of those kits only the DM5 Pro has MIDI out by the looks of it.
When you get your kit - make sure you get a bass pad patch or you'll wear through the pad itself with the felt pad hitting constantly.
For sticks - have a look at 5A or 5B (slightly thicker/heavier). I use Vic Firth Hickory 5B which has a wood tip. Hickory soaks up a lot of the vibration.