you guys should try
http://www.squakenet.com/computer_games/download.asp?game=746&title=The-Incredible-Machine had it on an old computer long ago. got up to around the 180-190 level out of 250 levels. looks simple, but gets extreme at those levels. I'd sometimes work on one puzzle for days. similar to the game linked above but increasingly difficult. thinking out of the box instead of what you learned in engineering class helps. had a little contest with a know it all contractor/builder who could go thru them faster. he lost. believe he pussed out around 40-50.