The problems you have sounds like a problem with windows, and not with Bryce itself. Had this with win98 when the RAM wasnt enough. (XP works better) About the DOF settings, one tip is to select the model you want to focuse on, then go to the rendering settings. Select "Premium" and click on the "Set to current selection". Dont worry about the Focal length, but to get the most realistic result, the Lens radius should be set to a maximum of 0.04. I usually use 0.02-0.03. I have used these settings on my images "Dreampeople part 2", "Pac Man" and "Panic". Check them out and see how the DOF looks on these. Hope this helps & good luck.

Rudolf Herczog
Digital Artist
www.rochr.com