Microsoft offers Virtual Server R2 as free download
 

Microsoft Virtual Server 2005 R2 is an ideal, production-quality tool for consolidating multiple workloads onto a physical server, allowing organizations to make more efficient use of their hardware resources. Built upon Microsoft Virtual Server 2005 SP1 and bolstered with new functionality, Virtual Server 2005 R2 enables IT organizations to enhance their administrative productivity and rapidly deploy new servers to address changing business needs through automated deployment and configuration of connected virtual machines that are easily administered with standard server management tools. Virtual Server 2005 R2 is an extensively tested and well supported virtualization solution that is supported both by the broader ISV community and by Microsoft in conjunction with its server operating systems and applications.

Supported Operating Systems: Windows Server 2003 R2 Datacenter Edition (32-Bit x86); Windows Server 2003 R2 Datacenter x64 Edition; Windows Server 2003 R2 Enterprise Edition (32-Bit x86); Windows Server 2003 R2 Enterprise x64 Edition; Windows Server 2003 R2 Standard Edition (32-bit x86); Windows Server 2003 R2 Standard x64 Edition ; Windows Small Business Server 2003 ; Windows XP Service Pack 2

Download at source: Virtual Server 2005 R2