OTMS Office

Legal answer: it depends.

If you have the full retail version, you will note that the EULA allows you to install a second copy on a portable device for your exclusive use.

But, if you have the OEM version, there is no such provision in the EULA.

You can read all about it here, in Microsoft's own words:

Activation and Product Licensing Policies How many installations can be made with one product license? Has this changed with the introduction of Product Activation? The underlying principles of Microsoft's software licenses have not changed. Microsoft's End User License Agreements (EULAs) have always stipulated the number of PCs that software can be installed on. Product Activation does not change that. Office XP or Office 2003 may be installed on one PC. The primary user of Office may also install one copy on a laptop computer for their exclusive use. To install Office XP or Office 2003 on more than these two devices, another license of the product must be acquired. Licenses for Office XP or Office 2003 acquired preinstalled on a new PC are single-PC licenses that cannot be transferred or installed a second time on another PC or laptop computer. Windows XP may be installed on one PC. There are no secondary use rights (e.g. no "laptop clause") in the Windows XP EULA. The aforementioned licensing terms have not been changed due to Product Activation. Some special licensing programs (such as the Microsoft Developer Network) provide additional licensing terms. Please check your specific license agreement or EULA for specifics. Re-installation and re-activation on the same PC can be done an unlimited number of times.

Of course, in the UK at least, there is the thorny issue of how legally binding certain provisions within the EULA are, but I'll leave that for another time...

HTH

Regards

S.P.