Hi,
There are a lot of documents describing different scenarios regarding installation in different existing topologies. Did you check "OCS_StandardEditionDeployment.doc" or "OCS_EnterpriseEditionDeployment.doc"? They tell you how to install OCS and how to prepare AD. There is also a special document about AD preparation (OCS_ADGuide.doc). If your test environment contains more forests, check "Deploying_in_a_Multiple_Forest_Environment.doc". And last, but not least, there is the "OCS_Planning_Guide.doc" discussing a lot of steps you should consider when deploying OCS.
HTH
Bernd