Windows XP Mode for Windows 7 makes it easy to install and run many of your Windows XP productivity applications directly from a Windows 7-based PC. It utilizes virtualization technology such as Windows Virtual PC to provide a Virtual Windows XP environment for Windows 7.
Windows XP Mode provides a 32-bit Windows XP Professional Service Pack 3 (SP3) environment pre-loaded on a virtual hard disk. Client virtualization software, like Windows Virtual PC is a pre-requisite to use Windows XP Mode.
System Requirements
Supported Operating Systems: Windows 7
Windows 7 Professional, Windows 7 Ultimate, or Windows 7 Enterprise.
Hard disk requirement: 2GB for installing Windows XP Mode. Addtional 15GB of hard disk space for the virtual Windows environment.
Note: You can use Windows Virtual PC to run Windows XP Mode on your computer. Windows Virtual PC requires processor capable of hardware virtualization, with AMD-V™ or Intel® VT turned on in the BIOS.
circa 445 mb in download per entrambe le versioni a 32 e a 64 bit...
http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=0e8fa9b3-c236-4b77-be26-173f032f5159