Sweet, thanks. I think I had found this a while ago but lost it, looks great!
...holy smokes, John Resig just replied to me. Thanks so much for jQuery, it has changed my life and is what made me become a programmer. (I now do client work for 20<20Thiel Fellows, and my startup has been in WSJ - none of which would have been the case if I hadn't started programming with jQuery!)
for an example of doing this with tar instead of zip check out https://npmjs.org/package/dir-tar-stream
In the example there you would .pipe() out to an HTTP response rather than a file, presumably.