A Flash 5 question.

I'm using flash 5 to make a game, and I'm not that good at programming, this may have an easy answer I dunno but I can't find it. Anyways, I'm trying to make it so that a character onscreen can walk infront of an object and then go past it and walk behind it but not walk over it, also theres an item which has to be collectable from the object. I tried a few things but I can't get it work.

I tried using depths to make the character go infront and behind at the necessary times, although this did work, when I went to a previous screen in the game, the character and sometimes the objects had duplicated themselves onto that screen and other strange stuff occured, It's probably because I don't quite know what I'm doing but if anyone can help I'd really appreciate it.

 

Last time I have developed in flash was 6 years ago.

I'd check out:
http://www.newgrounds.com/flash/
http://www.flashadvisor.com/forum/index.php