Hi Parmita,
The goal is to be able to install nodes in an environment where the DHCP server on the subnet is managed by another system. I think all that should be necessary to support this is to disable DHCP on windows 2008 server and configure it such that it does not answer PXE requests. (The existing DHCP server is already configured to send install requests to the windows 2008 server when nodes are PXE booted, so it is not necessary for windows server to actively respond during PXE process).
One piece of background: on windows 2003 we were able to configure it this way using the WDS administration gui and selecting (from memory) "Don't respond to PXE requests".
Jesse