This functionality is not supported in Flash Catalyst, too many backend systems to consider. You can add this via Flash Builder.
For a full feldeged contact form, see Tanya Hein's post: http://www.numencommunications.com/building-a-simple-form/
If you want just a simple mailTo link, add a Go To Url interaction to the button. Then in Flash Builder, you can edit the code from referencing an http:// to a mailto:email@example.com?Subject=Hello%20again. Flash Catalyst for some reason only supports the http protocal.
I am presuming Flash Builder is a separate program that must be purchased and not part of the CS 5 Production Premuim?
Yes. It is included in some of the suites. It does have a 60 day trial, so that might give you enough time to test it. You also might contact a local user group, maybe some one there might be able to assist with these quick additions.