[Typo3-dev] Javascript me please!

[Lasse Nørby]

Hi guys!
I'm trying to develop a new ext.. I need help :)

I want an IMG, expand.gif, to change to collapse.gif when the user 
clicks it, and then change back to expand.gif when clicked again.
How do i do this?? I guess it's something like: onclick="myFunction()", 
but it's the myFunction part I can't see through.
Please excuse my ignorence, but I am no programmer, and all I can do is 
the most basic javascripts like mouseovers etc.

Thank you!
Lasse Nørby