Adding Hulu Desktop to MythTV

cd /usr/share/mythtv
vi library.xml

Add the code below in whatever order you would like it to show in the Menu:

   <button>
     <type>STREAM</type>
     <text>Hulu Desktop</text>
     <action>EXEC /usr/bin/huludesktop</action>
   </button>

Now you can find the Hulu Desktop menu option by going to:
Media Library -> Hulu Desktop

UPDATE (04/11/2010):

After updating to MythTV .22 the above location of library.xml has changed.

It is now stored in:

/usr/share/mythtv/themes/defaultmenu

An alternative to editing the sytem wide menu's is to copy them to your home directory and edit those. MythTV will load your local copies first.

One problem to doing this is when you upgrade to a newer version of MythTV there may be new menu options that you don't get. You would need to recopy the files with the below procedure to get the new versions of the files.

First login as the user your MythTV runs as then do the following:

mkdir -p ~/.mythtv/themes/defaultmenu
cp /usr/share/mythtv/themes/defaultmenu/library.xml ~/.mythtv/themes/defaultmenu

Now you can edit the library.xml as noted above.