I got the IED05 Super-cheap. Its fun to play but the bundled software has some vile sounds and you soon get fed up with all that. The USB interface basially recognises the IED05 as a multi-axis joystick so any VST instrument is going to have to interpret joystick commands as midi notes
My first experiment was using a glovepie script I found here http://www.wibwobweb.com/blog/articles-by-me/using-the-ion-ied05-usb-drum-kit-with-midi-capable-software/
It worked well with a demo of Addictive drums, but I had problems with getting the retriggering right and I was constantly fiddling with values to get the sensitivity I wanted.
next I tried the excellent eTrigger ( www.etrigger.net ) There was lots of functionality here, but try as I might, there was no response at all from the low velocity ranges so I gave up.
I was beginning to think I was fighting a loosing battle, when I came accross DSP TRIGGER http://www.audiofront.net/dspTrigger.php