A BE-20 flight crew was given a descent clearance; but climbed 500 FT when the pilot flying inadvertently selected climb mode on the autopilot. The Pilot not flying noted the error and descent was initiated.

Narrative

We were in the cruise portion of our flight with the autopilot on over Lakeland VOR when Center gave us a descent clearance to 17;000 FT from 23;000 FT. I; non-flying pilot; set the altitude selector and was looking down setting the pressure controller when I noticed the aircraft climbing. I called it out to the pilot flying. When I noticed the deviation; the aircraft was about 150 FT above 23;000 FT. The pilot flying was extremely slow to respond and instead of disconnecting the autopilot and hand flying the correction; he relied on the autopilot for the correction. He selected the descent mode and the aircraft SLOWLY started the transition to the descent. By the time the autopilot made the reversal; the aircraft was around 500 FT above 23;000 FT. Center called to verify that we were descending to 17;000 FT and I advised we were in the descent at this time. No more was said by the Controller about our deviation. I believe the altitude deviation was caused by a lack of awareness on the pilot and reliance on automation. When you; as a pilot; push buttons you need to know what the buttons are and what to expect. Not to mention; first and foremost; flying the airplane. I think the automation is a great thing and the technology is even better and safer than ever before; but reliance on automation without confirmation is a very dangerous thing. The pilot flying pushed the climb mode on the autopilot and didn't confirm it with the instruments. The PFD tells you what mode is selected.