Tim/Deb, I assume you have standard 4x4 (or so) tiles set very closely together with the grout lines only 1/16" wide or so? Then there really isn't any easy way to remove that grout without damaging the edges of the tile. You might try simply cleaning the tiles and grout. Check with a local tile place about cleaners. There are cleaners available that can make your grout white again. Why didn't you get your builder to fix this problem for you before you moved in?