I'm not sure i understand you, but if you need to know how to open a obj file in Bryce, select from File tab Import Object..and navigate to the obj folder location. Usualy textured obj files comes with a mtl file and the textures in jpg format.To get the proper mats and a good obj to be opened in Bryce i suggest you to to open the obj in Daz , set the textures then use Export obj and select it for Bryce and "Collect Maps" must be on.After you imported sometimes you might be needed to click on "E" from that object to edit mesh and click again on the first ball to smooth the polygons.If you mean how to convert an obj into an obp and save it in brce database ,well i didnt worked with this and i can't help.Hope im not wrong.You can create a free account on Daz website ,go to Bryce forums section and post your questions there for more tips/details.The bryce community is very active there and David Brinnen and Horo (Bryce masters) are very helpful. 

Also keep in mind that older version scenes from Bryce  4,5,6 and perhaps some old obps might not import properly into Bryce 7.1.Feel free to post here or on Bryce forum, an obj or obp link found on Share CG which you can't import it and i'll try in Bryce to see if there is something wrong with the file.(im not an expert but at least i have some experience in bryce)

If it is about obj plants or trees then i can't help ,it's something about setting the alpha map on leaves which im not good on this)

Edited by cris333 on 01/23/13 06:34 AM.