Willie Dixon's in town for the "Poetry of the Blues" workshop at the Smithsonian, just one of a number of events in Washington taking place in observance of Black History Month. A free one at the Kennedy Center: folk dances from the Caribbean, performances celebrating Afro-Caribbean culture and history as they relate to Afro-American traditions. In the Theater Lab Saturday at 11 and 1, with demonstrations at 2 and 3. Call 254-3696. In the Smithsonian's Discovery Theater, storyteller Madame Griot and her sidekick, a spider, use music, song and dance to explore the traditions of storytelling in both African and American cultures. "Sing On, Ms. Griot" continues until February 28, Wednesdays through Fridays at 10 and 11:30, Saturday and Sundays at 1:30 and 2. Tickets are $2.50 ($2 for under 12) at the Smithsonian's box office: make reservations at 357-1500. And the Smithsonian's all-day cram session on the blues is Saturday, taught by artists who helped invent it: Washington's own blues poet-laureate Sterling Brown opens the colloquium at 9 and Koko Taylor, J.C Burris, Willie Dixon and Taj Mahal are a few of the bluesmen onstage talking their trade. Then there are Sunday blues at noon: a concert with J.C. Burris and two local blues artists. Tickets are $15 for the two-day workshop or $5 for the Sunday show at Baird Auditorium in the Museum of Natural History, Tenth and Constitution NW, and go on sale at 8:15 Saturday morning. Call 357-2700.