Ok, I've read some other posts, and I know that Bryce 5 only exports lattices, terrains, etc. (it'd be nice if it said that in the help file, wouldn't it?) Is there any way to change a boolean rendered object into a .3ds or anything else, or a way for Poser to import .obp? I noticed no one asked about Poser importing .obp....

Bryce booleans and primitives (including metaballs and trees in Bryce 5) are not exportable. They are native, not real meshes, and only resolve at render time. Bryce isn't a modeler and the 'building blocks' in Bryce are for scene enhancement. Bryce will export any meshes you've imported. If the .obp is made of imported meshes (nothing native) you can drop it in your scene, hit the little 'E' to get the smoothing editor, then CTRL-D to export as a mesh. OBP as a file format is not read by Poser or anything else other than Bryce.