Windows XP Mode was not designed for graphic intensive programs (see the notes section on this page: http://windows.microsoft.com/en-US/windows7/install-and-use-windows-xp-mode-in-windows-7).
However, just because your Windows 7 is 64 bit, doesn’t mean that your 32 bit software won’t work. There are several options to see if your CAD software will work on Windows 7.
1. Check the Windows 7 Compatibility List to see if your software is listed: http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=2394
2. You can try installing it and see if it works. Using the built-in compatibility settings may be enough to get your CAD software to work.
3. You can try the Application Compatibility Toolkit. Download links and instructions on use can be found on the Springboard Series Application Compatibility pages on TechNet: http://technet.microsoft.com/en-us/windows/aa905066.aspx.
Trying those methods before setting up a dual boot could save you the time and effort that will be needed rebooting to switch between operating systems.
Windows Outreach Team – IT Pro