All images available through the GovGrid Texture Store are offered through a Creative Commons License as indicated below.
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License
Basically you can use the images for any personal or commercial purpose except for selling them as is or offering them for free as is or for a cost on another website. You can however give them away for free in an Opensimulator-based virtual world or Second Life. The Sharealike only applies if you are creating textures from mods of these textures. Attribution is always appreciated but not required.