InfoPath 2007 Reusable Controls
When developing numerous InfoPath forms there are times when you need to create reusable controls. This easily can be achieved creating template parts with form controls.The following are a few links cover the process of creating template parts:
Documentation as shared on Microsoft Office Online: http://office.microsoft.com/en-us/infopath/HA101507461033.aspx
This is a lab from the MSDN developer center: http://msdn.microsoft.com/en-us/library/bb267331.aspx
QUICK NOTE: When you change the template part name in the Template Part Properties dialog box, the template part ID is updated automatically. This ID further distinguishes one template part from another.