New & moved PC deployments

Our organization has purchased several new Dell PCs with XP Pro preinstalled (each with its own license). I need to deploy these to users and add additional software they currently have installed. Also, their old systems will be moved to other users who use different software. What is the best way to complete these deployments without having to manually wipe and install everything many times? Sysprep and cloning? I was concerned about license keys. We are a non-profit so cost is important. Our network is a Windows Server 2003 Active Directory environment. Thanks for any help and ideas.