XP Mode is free to download so I don't think there is much to worry about using that on many machines. It is supplied with a free and Activated SP3. Where you might run into problems is when you use any operating systems (or other program) that require a Product Key to become Activated and that key is used multiple times.
It would pay you to look at any EULA or License ReadMe that come supplied.
Find End User License Terms for Microsoft Software Licensed by Microsoft or the Computer Manufacturer
Find End User License Terms for Microsoft Software Licensed by Microsoft or the Computer Manufacturer
7_Professional_English_b7a7153f-1a6c-498c-9350-c86926bb1aa9.pdf
END-USER LICENSE AGREEMENT FOR MICROSOFT SOFTWARE
MICROSOFT WINDOWS XP MODE
(WINDOWS XP PROFESSIONAL SERVICE PACK 3 IN VIRTUAL HARD DISK IMAGE FORMAT FOR USERS OF WINDOWS 7 PROFESSIONAL, ENTERPRISE AND ULTIMATE EDITIONS)
As read from the file C:\Program Files\Windows XP Mode\VXPEULA.txt
"GRANT OF LICENSE. Microsoft grants you the following rights provided that you comply with all terms and conditions of this EULA:
1.1 Installation and use. You may install, use, access, display and run one copy of the Software in a single virtual machine on a single computer, such as a workstation, terminal or other device (“Workstation Computer”), that contains a licensed copy of Windows 7 Professional, Enterprise or Ultimate edition. Virtualization software is required to use the Software on the Workstation Computer. The Software may not be used by more than two (2) processors at any one time on any single Workstation Computer. "
is it possible to run more than one XP Mode Virtual Machine