Microsoft recently released its Virtual Hard Disk (VHD) format:
Microsoft's Virtual Hard Disk (VHD) format can be used to collect an operating system, higher-level software and specific configuration details into a single package. A particular VHD image can be loaded into a virtual machine software such as Microsoft's Virtual Server product.
The VHD Test Drive Program mirrors an idea developed by virtualization leader VMware, an EMC subsidiary that for years has argued that virtual machines will ease software installation. The idea is that a virtual foundation means software experts, not customers, can worry about specific configuration and tuning details. Companies planning to provide trial software through the program include Symantic, Citrix, BEA Systems, Hewlett-Packard and Dell.