This video, via AfroDjMac, takes a look at how to use hardware synths in Ableton Live:

External instruments can easily be played inside of Ableton Live. Enjoy this Ableton Live Quick Tip in which AfroDJMac shows you how to set up an external instrument, such as the Synthboy ( http://ninstrument.com ). Once inside Ableton, it can be sequenced and effects can be added to further the potential of your hardware synthesizers!

You can find more from AfroDJMac at his site.