I have temporarily thwarted the leak. (I say "temporarily" because I don't want to get too cocky and tempt the revenge of mother nature, or anything. ;) I looped a great long bit of yarn around the hook in the ceiling, where it's leaking. The water is now running peacefully down the yarn, into the bucket, without a sound. This means smoother flow, less noise, and no splashing, which was the big concern because no matter how much plastic I put over everything it's still getting soaked when the bucket gets half full. So. Yay. :)
The window, however, is still leaking cheerfully. >.