Typically, Microsoft activation is tied to the hardware. I've never had to activate Office, since I've used Academic VLK. The activation mechanism is similar to Windows XP
During activation, the product ID and a non-unique hardware identification are sent to Microsoft. The product ID is generated from the product key used to install the software and a generic code representing the version and language of Office being activated. The non-unique hardware identification represents the configuration of your PC at the time of activation. The hardware identification does not include any personally identifiable information about you, any information about other software or data that may reside on your PC, or any information about the specific make or model of your PC. The hardware identification identifies only the PC and is used solely for the purpose of activation. Office can detect and accept changes to your PC configuration. Minor upgrades will not require re-activation. If you completely overhaul your PC, you may be required to activate your product again.
Product Activation works by verifying that a software program's product key, which you must use in order to install the product, has not been used on more personal computers than intended by the software's license.
From here. Thus, you can't use it both on the laptop and the desktop.
If you try to convince M$ representative over the phone that your laptop has suddenly died, and now you'd like to install Office on your desktop, then it will be a violation of the license agreement.