Walkable area in point and click game.

Nice example code, i was looking for something like this.
Any suggestions on how one should aproach the following:

I click somewhere on my nice adventure picture and then the character walks to that point. Now how can i make something re-usable to have the character walk a certain path, like in the Monkey Island games?

I've been wanting to make a point and click adventure but this issue has always kept me from actually making one.