I have only (knowingly) seen tambour beading a few times. To my untrained eye, it looks like a cross between crochet and latch hooking in execution; crochet with a hook that pierces the fabric. You crochet with the thread running on top, and beads or sequins added on the bottom. The tambour hook pierces the fabric from the top down, catch the bead, and pull the thread back up to the top of the fabric and do a chain stitch. Move the hook over the length of your desired stitch, and repeat. If you work with organza or another transparent fabric, you can see what you’re doing at least somewhat, otherwise, your bottom hand is threading the bead over the hook by feel.
I read something today that prompted me to go looking. Here’s a blog post by Cruz Barrientos, a couturier in Florida. He shows some of his early and later samples, front and back, and you can click on the pictures to enlarge. His link to Virginie Courdimanche (in Paris) doesn’t work, but here is her blog (in English). Her work is beautiful and delicate, and she has diagrams for a nice tutorial on tambour work. Barrientos also links to a Luxe.tv spot on La maison Lesage à Paris. All in French, but watching the 4:37 minutes of video rewards you with glimpses of beautiful work, work in progress, and towering shelves of beads and sequins and thread supplies I would love to see in person.
UPDATE 11/3/09: Please read the comments for more information from Robert Haven, an associate professor of Costume Technology at the University of Kentucky. I wrote a new post about tambour beading with the information he provided.