While announcing unlimited virtual machines for Windows Server 2003 Datacenter Edition and up to 4 virtual machines for Windows Vista Enterprise Edition, Microsoft also released Virtual PC 2004 with Service Pack 1 for free.
The product now includes a recent hotfix specifically designed for laptop systems, correcting several issues.
Download it here.
The company also announced the next version, Virtual PC 2007, will be released during 2007, will support Vista and will be completely free as well.
The virtualization.info Virtualization Industry Roadmap has been updated accordingly.