The form will be in the program folder for qRules 4.2, in the Forms folder - the default install location is here for a 64 bit Windows 7 machine: C:\Program Files (x86)\Qdabra Software\Qdabra Rules Library\Forms - you can always right click the form, select Design, and then preview it to use it.
I'm attaching a little EXE you can try to use for installing the full trust form - save the EXE someplace you can find it, then drag the form XSN onto the EXE (the Qdabra logo) - make sure you have all instances of InfoPath closed first (may need to check the processes in the Task Manager, as IP is sneaky)