May I use these textures for free?
Yes, the textures may be used for free in 2D or 3D computer graphics, movies, printed media, computer games and 3D models. When bundled with a 3D model or scene you are allowed to sell it as a package.
May I use your textures to make a (commercial) computer game?
Yes. You may use the textures from Goodtextures to make computer games.
I don`t know if you gain access to the other textures as well by registering an account. I haven`t tested it any further.
But the interest for such thread here is rather low as it seems. Maybe I won`t continue it here anymore.