Heat gas or charcoal grill. In medium bowl, mix ground beef, bread crumbs, taco seasoning mix and milk until well blended. Shape mixture into 4 (4-inch) patties. In another medium bowl, mix frozen potatoes and dip.
Cut 4 (18x12-inch) sheets of heavy-duty foil. Place 1 patty on each; top with 1/4 of potato mixture. Wrap each packet securely using double-fold seals, allowing room for heat expansion.
When grill is heated, place packets, seam side up, on grill over medium heat; cover grill. Cook 15 to 25 minutes, rearranging packets several times, until patties are thoroughly cooked.