It is easier to integrate with Cisco Call Manager 5.x and above version as CCM support SIP trunk to OCS 2007 server or via IP-IP gateway (router). I'm not sure Microsoft has release any supported documment on CCM integration with OCS 2007 or not. But I've tested the integration in a production environment.
For my this implementation; I've use Dialogic media gateway 2000 series (DMG2030). In a standard CCM 4.x environment, there will be a voice router which will be the interface with the service provider. The connections between router and CCM/media gateway will be using E1 link.
There will be some configuration need to be done at CCM as to route the inter-call between OCS client and cisco phone client.