The installation was quiet easy. Make sure you have a working Trunk SVN version of MythTV installed, the normal 0.20 will not work!
Download the newest mythweb3.rar file (the 3rd was the newest as I typed this) and unrar it into your myhtweb directory. Additionally you might want to update the player. I did it like this:
unrar x mythweb3.rar
mv MFPlayer.2.swf MFPlayer.swf
You will now find the player in the details view of a recording. Make sure you have enabled the mythweb.pl file to be executable, or else you will get errors like this from apache:
[Mon May 07 11:10:19 2007] [error] [client 126.96.36.199] (13)Permission denied: exec of '/srv/www/htdocs/mythweb/mythweb.pl' failed, referer: http://something.homelinux.net/mythweb/tv/MFPlayer.swf
This can be done with a simple
chmod ug+x /srv/www/htdocs/mythweb/mythweb.pl
After following a ticket on the MythTV SVN server for a few days I finally got an experimental but functional flash video player to work with my MythWeb installation at home. This is a great step forward, as it makes my PVR accessible to my parents and sister!
Update: The flash player has been added to the SVN repository, so that the how-to is not realy relevant anymore.