[Greasemonkey] Clicking an Image with coordinates

[Devin]

I am having a bit of trouble trying to click on an Image with certain 
X/Y coordinates.

I can trap the event, but I don't see a translated X/Y I can alter.

The result of clicking is a post, but I'm afraid I don't have a clue as 
to how to alter the form with the proper values.

I guess I could do an GM_xmlHttpRequest but I'd rather have a cleaner 
approach.

Any ideas?

Thanks
Devin