my friend having the same problem ^^
Set it when u start warcraft 3 , not a GAME warcraft 3 . When u start war3 its writed : Battle.net . lan , etc and there is a OPTION. Click on it and search quality texture and set it to max.
Its not you the map creater , so let the hosts creat the map and go play , stop say to them what they must do. Gaias ORPG is the best ORPG i played in warcraft III , so LET THEM CREAT THE MAP !