General Motors Corp., Warner-Lambert Co., Kraft Foods Inc. and Sprint Inc. have agreed to participate in an in-depth study to assess the advertising impact of a new technology that allows consumers to simultaneously jump from television commercials to Web sites. The Myers Report, a New York-based advertising industry newsletter, says Nielsen Media Research will conduct the three-month test in Massilon, Ohio, where a cable system allows viewers to immediately access additional information on products and services advertised on television. . . . Kraft Foods Inc. assigned advertising for Minute Rice and Shake 'n Bake to Foote, Cone & Belding from Young & Rubicam and assigned grated Parmesan cheese to J. Walter Thompson from FCB. All agencies are based in Chicago.