I tried to make an isometric game a while ago with r0j0's help. His isometric sorting algo was very good, but a little too cpu intensive with too many objects on the screen and ontop of that I hadn't collisions working also :/.
I found a really interesting game maker example here:
You need game maker installed to open the gmk file.
I let a friend compile it. I uploaded it to my dropbox -> Link.
I looked at the sourcecode via gmk file, but I couldn't port it to C2 :/
Maybe someone else could.^^
edit: arrow keys to move and z to jump