Alternate Marketing Networks Inc. said Thursday that it has purchased AdTrackMedia.com for an undisclosed amount of cash and stock. The move underscores Alternate's strategy to bolster its Internet offerings. In AdTrackMedia.com, Alternate gets a company that specializes in managing and serving Internet advertising campaigns for small- and medium-sized businesses. Alternate, Grand Rapids, Mich., has long specialized in developing advertising and marketing materials, including coupon-based programs. It also handles advertising and marketing for several GTE/Bell Atlantic regional and national telephone books.