Temperature i don't know about -- I generally get really warm when I sleep, so I usually keep a window open, but i haven't noticed that effect my dreaming.

I DO know that the noise produced by a fan ("white" noise) is condusive to sleeping. A doctor I once spoke to about sleeping problems told me that subtle background noises (waterfalls, waves, quiet thunder, etc.) aide in sleeping. I guess it can be hard to sleep when it is too quiet as well as too loud (obviously).