From the 2010 MSLT:
12. HOME AND STUDENT SOFTWARE. For software marked “Home and Student”
edition, you may install one copy of the software on up to three licensed
devices in your household for use by people for whom that is their
primary residence. The software may not be used for commercial, nonprofit,
or revenue-generating activities.
So you can install it on up to three computers, but you're not supposed to use it to write books that you intend to sell, or for marketing activities.
Edit to add: Activation - I don't know about this version, but the regular 2010 version has an offline activation option.