Well, when you're designing a form in Livecycle you can drop a "Submit Email" button in the layout. The palette for the button you are defining has a place to specify the email address and email subject associated with the button.
When the end-user (the user that is looking at your form in Adobe Reader 9) clicks that button, user is confronted with a popup asking if the native email client should be invoked (e.g., Outlook or Thunderbird). If the user is affirmative to that, the email client software fires-up and a new email is composed (and left open, not dispatched) with the email address and subject that you specified back in Livecycle.
Is that what you meant by your question?