From the E.U.L.A.:
YOU MAY:
1. Install and use one copy of the SOFTWARE on a single computer.
2. Install a second copy of the SOFTWARE on a second computer only if you are the main user of this computer (home computer or laptop for example).
3. Install the SOFTWARE on another computer only if you change your main workstation. In such a case you must uninstall the software from the old computer.
Subject to change, etc, etc, blah, blah...
That said, as long as you're not playing it on all three computers at once, and they're all your personal computers, you're fine.
