Borrowing, or Lending, most PC software is illegal. When you buy software you are buying a license saying you are able to play install etc.. Read the license agreement, you will see this(the 'product' is the CD and all files on it):
(came from the license on Red Alert 2)
YOU MUST READ THIS PRODUCT LICENSE (THIS "LICENSE") CAREFULLY. BY USING THIS SOFTWARE, YOU ARE ACKNOWLEDGING THAT YOU HAVE READ AND UNDERSTAND THIS LICENSE AND ARE AGREEING TO BE BOUND BY ITS TERMS. IF YOU DO NOT AGREE TO THESE TERMS, YOU MAY PROMPTLY RETURN THE UNUSED SOFTWARE AND RELATED MATERIALS TO THE PLACE WHERE YOU OBTAINED THEM FOR A FULL REFUND.
WARNING: THIS LICENSE CONTAINS "RULES OF PLAY" WHICH, IF VIOLATED, MAY AFFECT YOUR ABILITY TO PLAY THE GAME IN A NETWORK ENVIRONMENT. THIS LICENSE ALSO CONTAINS WARNINGS WITH RESPECT TO CONTENT TO WHICH YOU MAY BE EXPOSED.
GRANT OF LIMITED LICENSE. Westwood Studios, Inc. ("Westwood") hereby grants you (either an individual or an entity), the end user, the limited, non-transferable right to use this one copy of this software/cartridge product, and any accompanying electronic files and printed materials (collectively the "Product"), on any single computer or game platform only for your personal use and enjoyment. This License is your proof of license to exercise the rights granted herein and must be retained by you. Westwood may terminate this License if you fail to comply with any of the terms contained herein.
COPYRIGHT AND RESTRICTIONS. You have no ownership rights to the Product. The Product is owned
by Westwood and/or its suppliers, is distributed exclusively by Electronic Arts Inc. ("EA"), and is protected by the United States copyright laws and international treaty provisions. EA and Westwood retain all rights not expressly granted herein. You must therefore treat the Product like any other copyrighted material (e.g. a book or musical recording).
The Product is licensed to you only for your personal use and enjoyment and may not be used for any commercial purpose whatsoever. You may not loan, rent, lease, give, sell, offer for sale, sublicense or otherwise transfer the Product, or any portion of the Product or anything incorporated therein, including any screen display, sound or accompanying documentation, to any third party, nor may you permit any other person to use the Product in exchange for remuneration. Further, you may not place the Product on any computer, communications, or other system or network that would allow multiple users to access it. Notwithstanding the foregoing, in one case you may transfer your rights under this License on a permanent basis provided you transfer this License and the Product, including all accompanying printed materials, while retaining no copies, and the recipient agrees to the terms of this License. If the Product is an update, any transfer must include this update and all prior revisions.
You also may not copy, modify, adapt, translate, create derivative works of, publicly perform, publicly display, distribute, transmit, decompile, disassemble or otherwise reverse engineer or attempt to reverse engineer or derive source code from, all or any portion of the Product or anything incorporated therein, including any screen display, sound or accompanying documentation, or permit or encourage any third party to do so. Notwithstanding the foregoing, if the Product contains personal computer software, you may either (a) make one copy of the software solely for backup or archival purposes, or (b) transfer the software to a single hard disk provided you keep the original solely for backup or archival purposes. Further, if the Product contains a map or level editor, you may use the editor in accordance with the instructions in the accompanying documentation to create maps or levels for your personal use and enjoyment, and you may allow others to use such maps or levels for their personal use and enjoyment, but in no event may such maps or levels be exploited commercially in any manner, by you or any other person or entity.
You may not loan, rent, lease, give, sell, offer for sale, sublicense or otherwise transfer the Product