When creating or modifying an existing AS7 runtime, there is no way you can choose a Java Runtime Environment, like JBoss AS6 or Tomcat server adapters.
It bit me when I wanted to try AS7 with the new JDK7 CR1. It's a severly lacking feature IMHO.
So you need to :

• add the missing UI bits
• make sure AS7 is run using the selected JRE