If you can get the map name for the guild hall, it should be straightforward enough. Run the command
in-game before entering the guild hall, then zone in. That should print a map name, similar to "exp07_dun_drunder_fortress" in your chat window.
Once you have that, open up the _User_MapStyles.xml file and add the following, replacing NAME_OF_GUILD_HALL_MAP with the map name you found in the chat window.
<ImageStyle Name="NAME_OF_GUILD_HALL_MAP" displayname="The Fortress of Drunder" zonerect="-194, -145, 172, 129">
<ImageFrame Source="images/maps/map_exp07_dun_drunder_fortress.dds" SourceRect="0,0,752,564" />
Restart EQ2 and see if it worked. If it did, please post the full code snippet back to this page. If not, let us know what went wrong.