Adobe's License:
2.4 Portable or Home Computer Use: The primary user of the Computer on which the Software is installed may install a second copy of the Software for his or her exclusive use on either a portable Computer or a Computer located at his or home, provide the Software on the portable or home Computer is not used at the same time as the Software on the primary Computer.
P.S: I've have a copy installed on my main computer (PowerMac) and portable and have never run into any activation problems with CS2 or CS3.