Here is is a quote from the relevant section of the Photoshop CS2 license agreement:
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 her home, provided the Software on the portable or home Computer is not used at the same time as the Software on the primary Computer.
In Photoshop CS for Windows and Photoshop CS2 for Macintosh and Windows, Adobe has introduced product activation, which makes the two-computer policy strictly enforceable by preventing you from activating Photoshop on more than two computers. You can still install Photoshop on as many computers as you like, but only two copies can be activated. It is very easy to transfer activations from one computer to another, as long as the computers have an Internet connection. Even without an Internet connection, you can still transfer activation over the phone.
This information also applies to Adobe's other Creative Suite products: Illustrator, InDesign, GoLive, and Acrobat Professional.
Note: You can find the Photoshop EULA under the Legal folder in your Photoshop installation folder. There are several sub-folders for different language translations, with a "License.html" file under each one. For the US English translation for Photoshop CS2 on Windows, the file is located in C:\Program Files\Adobe\Adobe Photoshop CS2\Legal\en_us. If you purchased Photoshop as part of the Adobe Creative Suite, there will be a Legal folder under the Adobe Creative Suite installation folder.