I finally dug out the straw weaver I picked up out of curiosity, and made myself a belt! Woo! Now I can give Brian's back to him and still have something handwoven to keep my slippery silk robe shut. :D The belt is worsted weight cotton for the wrapping yarn, and doubled strands of the same cotton (in a different color) for the filler cord. I ought to have made the thing a teense longer -- I knew I was going to do that ;) -- but it functions, or at least ties around my waist. I have yet to test it on the actual robe it was meant for.
The entire thing took me about two hours. Whew. The next one will be quicker (assuming I manage to convince myself to make a next one; my track record of repeating fairly easy tasks isn't good ;)), probably; and I can think of a lot of neat things I could do to make future belts fancier...