Backwards application compatibility in Windows 7 and Linux
Recently helping with Windows 7 migrations, I've taken a look at "XP Mode" in Windows 7. It was hyped up by everybody as offering backwards compatibility in Windows 7. Much to my surprise when I got it downloaded and installed, it's simply an XP virtual machine running with VirtualPC, with a very generic Windows XP Professional installation inside of it. I think it should really be called "XP VirtualMachine" instead of "XP Mode". XP Mode implies that it's more integrated into Windows 7, which it is not. It's a separate operating system, which requires its own updates, etc. I can see why it's offered, as it offers a completely separate environment because Windows 7 cannot run some older specific applications. Thankfully, "XP Mode" is free.
Windows does have a "compatibility mode" as well (simply right click on any executable, and under the Compatibility tab you can choose what version of Windows to emulate back to Windows 95, but I've had very mixed luck getting it to actually help applications or make any difference.
Migrating to any operating system is always going to be a challenge, it's just a matter of how much work it is. It could be minimal, or a lot, depending on the specific applications needed. There's been a lot of fuss and rumors about migrating from Windows to Linux, too. And I have to mention that there are a lot of similar issues for users migrating from Windows XP to 7, as there are from Windows XP to Linux. Both paths require a learning curve. Both have issues with application compatibility.
What many don't realize, is that Linux has TWO options for application compatiblity. Linux offers Wine, the Windows Emulator. It can run Windows applications, allowing each to use its own DLLs without affecting other applications, as well as run in whichever Windows version you specify for it. The best part of this is that it can all happen to the same filesystem structure (all files are stored in the user's home folder, in a directory called ".wine").
Linux also offers Virtual Machine capability, with a couple different products. The one that is most like "XP Mode" is probably Oracle VirtualBox. There are packages available for the main distributions for easy installation. VirtualBox can run a Windows virtual machine, allowing complete access to hardware and everything else. So if you need 100% XP compatibility, VirtualBox should be your answer. The drawback of this is the same as "XP Mode", where you will have to maintain updates because it's a separate operating system. Wine works well in a lot of cases too, and is much faster and doesn't require booting a VM as applications are opened on the fly, however compatibilty varies. Some applications simply don't work. Others work flawlessly. Check the Wine compatiblity website to check on compatiblity.