I am looking for a bit of help. I want to start recording drum tracks with E Drums. I have seen posts about using E Drums to trigger drum sounds but I would like to know how this is done and what equipment and software I would need to do it? 

I have a Roland TD4 kit and Sonar X1 Studio DAW and I have recently bought a Motu Audio Express Interface. Do I have what I need with this combination of hardware and software or do I need to invest further?

The link below lists the software package that I have.

http://www.roland.co.uk/products/productdetails.aspx?p=1134

do you have session drummer 3 in studio ?
I don't think you do.
this is how I do it:
http://www.youtube.com/watch?v=TjZS61Wg-XY

I tell people often that the extra 100.00 it is for producer is way worth it.
your going to have to invest in a drum software

All you need a is MIDI interface (I don't think the TD4 has USB) and connect the MIDI cable from the TD4 to it and then you can trigger any sounds on any softsynth in Sonar that you have. The TTS-1 has some drum kits. They may or may not be as as good as the ones on the TD4. The Cakewalk UM-1G is an inexpensive MIDI interface is you only need one MIDI port. 

Charlie - Nice little video, short and to the point, with all the info.

Djspahead - I use the drum brain to record drums, just a midi lead from the output of your drum brain to the Midi in of your Motu,
recording on to a midi track in Sonar.

A quick trick for getting zero latency without too much faffing, and not having to worry about drum sounds in your daw (at the point of recording), is to also run an audio output from your daw (via the motu) into the aux in on your drum brain and then use your headphones on the drum brain, using the soudns on the brain.