I have civilization 4 installed and it works great. When I try to install beyond the sword it tells me that civilization 4 is not installed properly. Ive tried uninstalling and reinstalling it a dozen times and I continue to get the same message before it lets me install BTW. What can I do?

What operating system are you using and what kind of hardware do you have (video card, etc) ?

I am using windows XP. It shouldnt have anything to do with my system not being able to handle it or anything. The game was actually on my computer a few months ago when i borrowed it from a friend and I deleted it. My computers video card and everything else is real good and can run pretty much anything. Now I bought my own copy of it and it wont work. Ive tried uninstalling and reinstalling in safe mode too and that doesnt do anything.

Are Civ4 and BTS cd/dvd versions or did you download them?

Both are the CD versions

Does original Civ4 show up in Add/Remove Programs list?

If not then you're missing a registry key for Civ4. I posted it here: http://forums.civfanatics.com/showthread.php?t=249755

Yes it does appear in the add/remove programs list. Thats how I uninstalled civ4 before reinstalling it. It reinstalls fine, plays great, but then when I try to put on this expansion it says that civ4 is not installed correctly.