Small Images at 3207 O St. NW has 6-foot-tall black-and-white posters of Marilyn Monroe, James Dean, Charlie Chaplin and Albert Einstein, plus other heroes--hang them on your wall for only $4 ... Nadek Corp. can help Santa get ready for the holidays, and at good prices. Two mothers who live on Capitol Hill, seeking high quality toys at reasonable prices (a little over wholesale), have opened a catalogue business. You can't get it in the mail--this one's in a dining room. Visit Thursdays or by appointment to view the selection of Brio, Galt, Kouvalis and Semper toys. Nadek, 1016 Massachusetts Ave. NE. 543-1226 or 544-7746 ... Someone teaches circus dogs how to do tricks. Someone was Benji's mentor. Someone trains canines for commercials. What if your mutt could do all that? The imagination soars. The first step along the road to stardom is Mr. Lucky's Trick Dog Training Book (63 pp.), $4.95, for people who want to train a dog to perform tricks on command. Any healthy dog six months old or more can learn them, says the author, who has not only trained dogs for movies, TV and commercials but also dogs for police work and dogs that serve as "ears" for the deaf. Denlinger's Publishers, P.O. Box 76, Fairfax, Va. 22030, or call 631-1500.