Digital BW, The Print

Since the release of CS (v1) on Macs Adobe has instituted a software
activation routine. The single user license allows for two installs
since many users will have a desktop and a laptop. So you can install
CS3 on two machines. Once activated on both, you cannot install PS on
another machine unless you A) purchase another serial number or B)
first deactivate one of your current installs.