Hope Everyone know that Exchange 2007 SP3 can be installed on a Windows Server 2008 R2
Lets see how to do a typical Installation

Prerequisites for Hub , CAS , Mailbox – Typical Installation
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Open Window Power Shell
Import-Module ServerManager
Add-WindowsFeature RSAT-ADDS,Web-Server,Web-Metabase,Web-Lgcy-Mgmt-Console,Web-Dyn-Compression,Web-Windows-Auth,Web-Basic-Auth,Web-Digest-Auth,RPC-Over-HTTP-Proxy;
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Good to know
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For Hub
Add-WindowsFeature RSAT-ADDS,Web-Metabase,Web-Lgcy-Mgmt-Console

For CAS
Add-WindowsFeature RSAT-ADDS,Web-Server,Web-Metabase,Web-Lgcy-Mgmt-Console,Web-Dyn-Compression,Web-Windows-Auth,Web-Basic-Auth,Web-Digest-Auth,RPC-Over-HTTP-Proxy

For Mailbox
Add-WindowsFeature RSAT-ADDS,Web-Server,Web-ISAPI-Ext,Web-Metabase,Web-Lgcy-Mgmt-Console,Web-Basic-Auth,Web-Windows-Auth;

For unified Messaging
Add-WindowsFeature RSAT-ADDS,Web-Metabase,Web-Lgcy-Mgmt-Console,Desktop-Experience;

For Edge
Add-WindowsFeature RSAT-ADDS,ADLDS;

For CAS and HUB
Add-WindowsFeature RSAT-ADDS,Web-Server,Web-Metabase,Web-Lgcy-Mgmt-Console,Web-Dyn-Compression,Web-Windows-Auth,Web-Basic-Auth,Web-Digest-Auth,RPC-Over-HTTP-Proxy;
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Exchange Server 2007 Service Pack 3 
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Extract it – Run the Setup

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Choose the Organization Name :

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Choose Yes , If you have Outlook 2003 , Cause Here where we decide PF database to be created or not.
But anyways if you choose No. It can be created later .

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Click Install -
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Great !!
You Installed Exchange 2007 SP3 in W2k8R2