Yes, I figured out about nesting layers, so I got the alignment working.
I couldn't get the resizing of the wheel.png to work the way I wanted, so I just adjusted the 'box' so that it worked for the tallest wheel.png when they were all adjusted by width.
It's not totally perfect but with such a variance in wheel.png sizes and shapes I think it looks pretty uniform.
alt text
alt text
Now to run it on all the other systems and hope it comes out OK.
Edit: Just tweaked the box so rather than having its own border in the png it just uses the stroke feature to match the border on the screen shot.
Not thrilled with the banding that gets introduced with skyscraper.