A fantastic source for the proper diet for cavys is right here:
http://www.guineapigcages.com/forum/...arts-info.html
Make sure to read all of the stickies at the top of each forum of this site. They contain loads and loads of great information about caring for guinea pigs. After you read all of that...you'll know more about the proper care of cavys than you ever thought possible (believe me...I speak from experience!).
Good luck with your new piggies and post pigtures for us to "ooh" and "aah" over!