[plt-scheme] Graphycs with Scheme

Hi all.

I'm programming a game with some friends for a project we have to do  
on Scheme.
So all our work is on a canvas... With a map that moves , and the  
object that stays put. (Like mario).

Right now i am working on my object, that should move with the mouse  
click,( You click the object goes up, otherwise it falls down) .  That  
is not supposed to be to hard to do.

But the object in question, has to change shape when going up, and  
when going down. (Same example with mario, when he jumps, he puts his  
hand up).

What's the best way to do it. I had an idea but didn't know if it was  
possible. It was, to Put Two pictures on the same location moving both  
of them at the same time, and when you click, the old picture becomes  
invisible (Is that possible) and the new one Visible, And visa versa  
when you unclick. If the visible/invisible command exists, if someone  
could please tell me how to use it :D or where i could read about it,  
I'd appreciate it. If it doesn't If anyone has a better Idea, I'm open  
to all suggestions.

Thank you

Marc