Maybe I'm missing something. I don't quite follow where you are wanting to use an interrupt exactly. On the receiving end, VirtualWire uses a timer interrupt to continuously sample the receive signal and has a state machine to recognise, decode and store the received message. You don't need an additional interrupt to make that happen.
If you are looking for an asyc notification that a message has been received by VirtualWire, you could probably hack something into the VW code, but it would not wind up being any faster or more efficient than polling the receive message function already is.