Microsoft has made available a trial version of Windows 7 Enterprise in both 32-bit and 64-bit versions. According to Microsoft, "It is designed specifically for IT Professionals, so that you can test your software and hardware on a final version of the product. In addition, it provides the opportunity for you to become more familiar with the key improvements over previous versions of the Windows operating system, and experience firsthand how Windows 7 can make your PC environment more productive, secure, and manageable." The free trial version is available as DVD images or a VHD (virtual hard disk) file for use in Virtual PC or Hyper-V Server.
Keep in mind that Windows 7 Enterprise is equivalent to Windows 7 Ultimate.