There are multiple ways this can be accomplished.
One way is through script. The attached demonstrates the use of an exit event to push data from firstName in subform1 to firstName in subform2. It also demonstrates the use of a calculate event to pull data from lastName in subform1 to lastName in subform2.
There are other techniques when a data source is involved.
See http://help.adobe.com/en_US/livecycle/9.0/designerHelp/index.htm
Using Designer ES2 > Working with Data Sources > Binding fields to a data source > Ways to show the same data in multiple places
Steve