Well the XP Mode for Windows 7 is still kicking around. In fact Microsoft has just released it to Release Candidate phase.
The Win 7 add-on is designed to allow legacy applications to operate in a virtual mode. This is intended to allow for an easier transition to the new OS from XP.
This development is designed to allow Microsoft to finally stop support for Windwos XP. There are some prerequisites that will hinder this app though. For one, older systems that do not have either AMD-V or Intel's Virtualization will not be able to use this.
You will also need a virtualization engine like Virtual PC. There is no word yet on if this will work with other virtualization engines though.
If you are interested you can grab this here