One feature of Windows 7 that you may not have heard of is Windows XP Mode on Windows Virtual PC. These allow you to use hardware assisted virtualization (if your processor supports it, and you have it enabled in your BIOS) to run guest operating systems. Windows XP Mode is a free copy of Windows XP Professional SP3 that runs on Windows Virtual PC. This is a big improvement over Virtual PC 2007.
If you are unsure if your system supports hardware virtualization, you can download this tool from Microsoft to let you know for sure.
There is much tighter integration between the Windows 7 host and the Windows XP Mode guest, which makes it easier to run legacy applications (like the Cisco 32-bit VPM client). Of course, I am hoping that we implement Microsoft DirectAccess, which lets you use a Windows 7 client to talk to a Windows Server 2008 R2 server on a corporate network without using a VPN client.