Hi
What you are saying is possible to do in a Dialog.
Create a Dialog
Add a Stage
Add a Page withing the Stage
Add a Prompt / Response withing the page - and name this as "CreateActivity"
Add your question and choose radio button for the question within the Prompt / Response - 0=yes, 1=no
Add another stage
Add a condition under the second stage
Check if the Local Values > CreateActivity > response value > Equals > 0
Create Record
Choose Appointment and Set Properties
Activate your Dialog
Thanks and Regards
AniMandal
http://xrmadventures.wordpress.com/