I am reading your inquiry for the first time on 01-29-02, if you haven't gone yet I would like to share some info with you. And I hope I can help with this.
At Dunns River Falls, all the tours and guide seemed to be the same. You could probably (as it was a few years ago when I was there, and I don't think it would have changed) just get a taxi and have them take you there, and just hook up with a guide. They usually take a large group at a time. They are willing to hold on to everyones cameras and lead the group in a serpentine fashion up the falls. They also will take your photo with your camera at the desired spots, and they don't get them wet. Once atop the falls there is a staircase you can walk down, back to the cabs.
You may want to invest in some water sandals, sport type, or use some old tennis shoes you can toss out when you are done, because they will be soaked. The water is cold at first but you get use to it soon.
If you knew all of this, please excuse the time I took from you.
Otherwise have a great time.