I use GeekTool a lot, and one of the things I use it for is to display my new email messages on the desktop. To do that, I use this AppleScript:
In GeekTool, I created a new entry and set the pop-up to Shell. On the Command tab, I entered the command as osascript /path/to/mailcheck.scpt (replace with the path and name of your own AppleScript).Mac OS X Hints
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