Joining the crush of companies offering free Internet home pages, Warner Bros. launched a joint publishing venture that seeks to attract users by offering access to free content drawn from the studio's various entertainment properties. The effort is a direct challenge to such sites as GeoCities, Tripod and Go Network, the monster venture launched this week by Walt Disney Co. and Infoseek. Burbank-based Warner teamed with home page publisher FortuneCity Inc. to create this online community, called Acme City, which offers themed "neighborhoods" that let fans build customized sites by using photos from shows, including "Friends," "Buffy the Vampire Slayer" and "La Femme Nikita." Later this year, users will also be able to add music, animation and film clips to their sites, said Richard Jones, founder of New York-based FortuneCity. Warner Bros., which will take an undisclosed equity stake in privately held FortuneCity, will spend more than $100 million to promote the site.