Yes it is copyright infringement, though alot of companies are lax about it unless you gain ALOT of popularity, as in if everybody knows it (what you've made that is), chances are you'll get a message from the lawyers, it's illegal no matter how you cut it, but as long as you're not making a commercial game, and your giving credit where credit is due, often times they just look the other way.
Don't screw with LucasArts though, they're hardasses.