Best way is to print the slides to PDF for import into iPhoto (if you have a Mac.) Then sync those over to the Touch.
Alternatively, convert your slides any other method into photos for the Touch on both Mac or PC.
You don't get builds and stuff, but who cares on a small screen. The main thing is that the unit is very responsive, and it's easy to go back and forth thru your slides.
Another way would be to export your presentation as a Quicktime video, and play that on your Touch so you could get transitions. But I would imagine pausing and unpausing (to answer questions and whatnot) would be a pain.