Adding "Custom Header" capabilities to custom template

Hey all.

Is there a guide somewhere that can show me how to add the new custom header capabilities of WP3 to my custom theme?

You know, like in the twentyten theme where you can choose a different header image or upload your own via admin panel. How do I add this function to my own theme?

I’ve googled for ages now and can’t find anything that works.

Cheers for any help.