Install Project Server 2007 in Windows Server 2008
This article discusses the requirements and steps for installing Microsoft Office Project Server 2007 in a stand-alone Windows Server 2008 environment.
https://technet.microsoft.com/en-us/library/cc531331.aspx
If you are looking for reasons why you should deploy PS 2007 on Windows Server 2008, check this white paper:
When planning an implementation of Microsoft Office SharePoint Server 2007, deployment on a Windows Server 2008 platform offers a unique set of advantages. New Windows Server 2008 capabilities improve the management, security, reliability, and performance of Web applications, such as those in deployments of SharePoint Products and Technologies. This paper describes how these new features address important issues that face organizations that deploy Web solutions with SharePoint Products and Technologies.