just played this. fun idea. horrible hit detection. I could not land on that blasted sign at the trash dump wound up landing on it by accident.
I'm rather new to flash game making myself. so I'll point you to a better hit detection system I've been messing with from a tutorial. I've found it to be very reliable after some tweaking. basically you compensate for flashes calculation delay by checking where your going to be on the next frame, adjusting the locating so it's not inside the platform, then moving the player sprite to that location. eliminates the passing through walls, and not landing on things problems.
http://www.emanueleferonato.com/2007...-flash-step-2/