I made a little tutorial here after reading JenC's thread... This should work for everyone.
Give it a try and let me know how it goes...
http://fuk.ca/wmvprotection/
Note that this protection works on with cookies... after you visit the authorized URL you will be able to access the file even via the hotlinking domain for 24 hours because the cookie lasts 24 hours.
Clear your cookies to after visiting the content url to experiment with it.