picking with selectbuffer slow -- software picking?

hello, i am using the opengl select rendermode to perform picking on my objects. unfortunately the framerate drops from about 200 to 90 on my GF7300 as soon as i render to this selectbuffer. is this normal? why is the selectbuffer so slow? now since i use a lot of alpha-textured objects anyway, i was thinking if a software approach to picking would be better in my case. would that be possible? if so, how? thanks!