I followed the install d2 guide posted in the GH unified sticky and got normal d2 installed fine, i now want to get xpac installed as well, however when i put the disk in it tells me to install diablo 2 first, yet it's already installed.

How do i install d2 LOD without using the disk?? only the cd keys?

Thanks!

Did you already give this guide a go?
http://forums.d2jsp.org/topic.php?t=32373257&f=21