Gimp makes it really easy to create multi-res .ico files. In fact, this is one of the few areas where Gimp beats Photoshop hands down.
The trick is to use multiple layers with different sizes.

Here are the basic steps.

Greg was having so much fun playing with the face tracking software that he didn't tell me what kind of camera he just got, but while he was doing that I was taking snapshots.
[g2:5279]

This is a simple tutorial on how to create a ruber stamp effect like
the one pictured below in Gimp.