Knight-Ridder Inc. and Softbank Corp. invested a combined $12.1 million in Zip2 Corp., a closely held producer of Internet-based yellow-page business listings. Palo Alto-based Zip2 said it will use the funds for product development, international expansion and other uses. The company is expanding its online services to include real estate listings, classified advertisements and arts and entertainment guides. Miami-based Knight-Ridder said it will have a seat on Zip2's board. The newspaper publishing and business services company said it will use Zip2's real estate listings for seven of its online services. Tokyo-based Softbank is the world's largest publisher of computer-related magazines and books. Zip2 was founded in January 1995.