Microsoft has released Virtual PC 2004 Service Pack One. If you're using VPC2004, you'll want to review, download and likely apply this update.

• Get the VPC 2004 SP1 download here
• Get the Service Pack Readme file here

Lots of fixes and improvements in this service pack, so be sure to take a look.

More information about the service pack from the Microsoft site:

SP1 also includes the following additional software updates

• A new Virtual Disk Precompactor. A utility that is designed to "zero out"—that is, overwrite with zeros—any available blank space on a virtual hard disk.

• Updated version of Virtual Machine Additions.

• Update to support TCP segmentation offloading. Prior to SP1, if TCP Segmentation Offloading was activated, some virtual networking features would not function correctly. With SP1, if your physical network adapter supports TCP segmentation offloading, you can activate TCP segmentation offloading, and virtual networking will function correctly.

• Update to support Group Policy Software Installation. For more information about Group Policy Software Installation, see Help and Support Center in your Microsoft Windows Server 2003 operating system.

• Update to change the default performance option from Give processes on the host system priority to Run Virtual PC at maximum speed.

• The hotfix described in article 833506, which describes how Virtual PC 2004 may stop responding when a virtual machine is started, in the Microsoft Knowledge Base.

Microsoft Virtual PC 2004 Service Pack 1 (SP1) contains the latest software updates for Microsoft Virtual PC 2004 that improve the reliability, performance and manageability of Virtual PC. Updates have been made to improve the performance of Windows XP Service Pack 2 as a guest in Virtual PC, to improve the manageability of virtual machines when used with SMS 2003 Service Pack 1, and to provide support for running Windows Server 2003 Standard Edition as the host operating system.

Some of the fixes included with SP1 have been previously released as separate updates. This service pack combines them into one update.

Important: You must shut down or turn off all guest operating systems before installing SP1. This ensures that there are no virtual machines in a saved state. This is important because saved states are not compatible between SP1 and all previous versions of Virtual PC 2004.

Service Pack 1 includes an updated version of Virtual Machine Additions. You should update the version of Virtual Machine Additions on all virtual machines where Virtual Machine Additions is installed. For more information, see "Installing Virtual Machine Additions" in Virtual PC Help.