that did the trick, thanks!
i had some problems at first but after updating to the latest releases of firefox, mplayer & mplayer-plugin it's working.
for the record, here's the releases of each component that comprise a working configuration for fedora core 3:
greasemonkey extension 0.5.3 (installs directly from their web-site)
pklaunch-0.6rc3.user.js (install per instructions)