Assuming you want to move the whole ePO installation and upgrade, then don't try to do it all in one step.
Move 4.6.6 to the W2K8 server first, this article may help:
Then upgrade to 5.1 on the new server.
However the question is not entirely clear if you are looking to move just the 4.6.6 database or something else.
Working ePO : Windows 2003 Enterprise x86 / eP04.66
Working DB Server : Windows 2003 Enterprise x86 / sQL 2005
Newly built ePO / DB Server : Windows 2008 R2 Ent x64 / ePO 5.1 / SQLServer 2008
Need to Migrate everything from existing server to new server....hope this clearsAppriciate your responce.
Further, the DB name changes and the Hostname and IP too.
With all those changes proposed at once you will surely break any existing agent to server communication.
As I mentioned before - don't try to do it all in one step.
Move the 4.6.6 ePO installation to the W2K8 server first, this article may help:
Make sure it's working then upgrade in-place to 5.1 on the new server.