This is a database compatible with Underlord. Just un-rar and copy into the database folder of the custommaps folder you already have for lilith. Rename your original (maybe lilith.arz) to SAVE_lilith.arz and then rename lilithunderlord.arz to lilith.arz.
Start Lilith in a custommaps game with Underlord installed.
This is only the database, you need all the other files (resources) from Lilith1.1.
I tested the first two quest and leveled up and check all masteries. It should be good to go. The only thing is this version gives 4 skill points per level up. Sorry.