Do you use the most recent version (at least 0.5, but better 0.6)? If not, then you can't directly edit these files.
>>Here<< you can download the most recent version.
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RunUO RemoteAdmin - Control your shard remotely and keep an eye on the page queue
MulEditor - Modify gump, art, tiledata, multimap, localization files and
map/statics.
CentrED - A Client/Server based
multi-user map editor.