Don't think they have a demo version but I've seen some of the work done in Xenodream and just from some of the gallery images alone, if I had the money I'd purchase it. Try the following link if it helps:
http://www.xenodream.com

or you could try the freeware program Apophysis which I use and I find it an excellent one for beginners as well as advanced users.

http://www.apophysis.org

Even Ultra Fractal has a free trial download
http://www.ultrafractal.com

Hope this helps
Regards

shemia