Writing user stories for acceptance test driven development

[Kirsten Greed]

Hi All
 
Can anyone point me to a good mailing list/ book/ person on how to do
acceptance test driven development
In particular how to write user stories and the steps for user stories.
 
We have got Specflow working nicely and want to write a service for a
shopping cart to use
 
We are able to articulate "As A ..., In Order to ... So that"
 
but having trouble getting the flow articulating Given, When and Then
 
Thanks
Kirsten