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).
From the E.U.L.A.:
YOU MAY:
...
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).
...
4. Use the SOFTWARE via a network, only if you have purchased an adequate number of licenses. The number of users must not exceed the number of licenses you have purchased.
translation: if you have two computers on your personal lan that you are the primary use of, you may install on both. you shouldnt install on computers that do not belong to you. and if you happen to install on a friends pc, then you will definately want to make sure it is uninstalled when before you leave.
regardless, there are tons of posts in this forum where people have asked this question. even ironclad team members have stated that lan games using one copy is fine as long as its your lan and your computers.