assuming you have a data folder and an IJL15 of some sort:
Go to your data folder in the mabinogi folder and place you maps in gfx\gui\map_jpg
overrite any existing. If the folders don't exist, create them. data>gfx>gui>map_jpg
that should be it. Taken from busaccident's Placeholders. Couldn't think of the directories off hand. xD
Thank me if I helped!