You could use the $$m-Exporter from ventilator, but it works only with blender up to version 2.49. It exports all (selected?) objects as seperate models of a level.

http://www.puppenheim.org/
http://www.wuerfels-welt.de
Old Game Tutorial: http://www.puppenheim.org/MITutorial.zip
Free Game Editor: http://puppenheim.org/AlienalsWeihnachtsmann.zip
http://www.puppenheim.org/blender_starting_main_settings.txt