D2: LoD installation problem

[spectr3]

I popped in the LoD CD, and it says i can't install it because it requires Diablo 2 installed on my comp first. Funny thing is, D2 IS installed on my comp (the files are all there) and I can play it fine. The only thing I did was reinstall windows. I'm guessing that overwrote some registry setting. I would reinstall D2 from the CDs, but I left my CDs at my parents' place. Is there anyway to make the LoD CD think I have D2 installed (with a reg hack or whatever, without the CDs)? Thanks in advance for help.