I think you might be able to use [URL=mailto://firstname.lastname@example.org]Your Name[/URL]. I`m testing this in my signature right now.
I just clicked the link and got the wonderful prompt from Vista that the web page wanted to open my Outlook. So the technique should work for email clients.
The "mailto:" tag opens up your default email client to send a message. If you want a URL to a link, then don`t use the mailto: tag.