Francis Coppola's "Gardens of Stone," starring James Caan and James Earl Jones, didn't click with audiences in movie theaters, but it's generated surprising interest among video renters. It's No. 10 after just two weeks on the Billboard magazine rental chart. "Superman IV" is the other hot new rental, climbing faster that a speeding bullet--to No. 7. "Lethal Weapon"--No. 1 for six weeks--looks as if it will be the rental king through the end of the year. "Roxanne," a new release not yet on the charts that was well received in the theaters and by critics, will be a serious challenger for the top spot in the first few weeks of the new year. "Lady and the Tramp" still leads the sales chart, which measures sales to retailers and distributors. Other sales charts: "An American Tail" and "Sleeping Beauty" trail "Lady" on the kidvid chart; "Callanetics" is the health and fitness chart champ.