Can someone tell me or point me in the direction of documentation as to how to configure a H.323 Trunk between a CUCM6 and a CME4?
On the CallManager you will create a H323 Gateway. You will need to configure the route patterns of what you want to go to CME pointed at that H323 gateway.
On the CME you will need to create a VOIP Dial Peer that points to the CallManager.
Example - If the extensions you wanted to dial from CME to CM were in the 1XXX range and the IP address of the CM was 10.10.10.10 you could do this
dial-peer voice 1000 voip
description ** Calls To CM **
session target ipv4:10.10.10.10
Hope that helps.