Download the mod tools. Read the documentation about layers and game modes. Open up a level and create an XL mode for it.
You should try asking Darth Derky for a better explaination on how to do it. You can also check out www.gametoast.com for modding help. I think they could answer your question better.
(I may not agree with thoughts posted under this name)
Looking for a mature clan? Checkout www.rdhclan.net
email/PM me for more info
I think there is no such person as Darth Derky... But I made a XL mod too for Utapau... But that was with hexediting, so like Zerted said, download the mod tools, read the documentation and make your own map with XL in it!
I'm working now getting the Rhen Var: Harbour and Geonosis: Spire maps in SWBFII.
But I have stopped working on those, untill there is a fix for BF2_modtools.exe, a .exe you put in your gamedata directory and play SWBFII and it will list all things that are wrong with your map.
Darth, if you manage to get the new maps, if you post them on here or somewhere else, can you include the '.lvl' things too? Because just 'addon' is not user friendly..