Im new to Bryce- how and where to I open/install .opb s? plz help!

Click on the triangle/arrow beside the word Create on the upper edge of the screen. When the dialog box Objects opens, choose the category you want the object to be in (Installed or User, Boolean objects and so on), click on the word Import. Locate your obp file in the file browser, click yes. That's it. When you want to use the obp in your scene, just repeat the first step and then highlight it among the others and click on the checkmark. When you want to add an object you created in Bryce, repeat the first step and click on Add. The object will be added at the bottom of the category you're in. And then you can Export it, if you want.

If you want to use an obj or 3ds file in Bryce; Click on file menu at top left hand side of the screen. Click on import object... and choose which object you want it to import. Hope it helps, TT.