Rome Total War installation error. Help please!

I just purchased a used copy of Rome Total War off Amazon and when I tried installing it I get an error that say no prior detection of Rome Total War, program will now be terminated (or something in that nature). It pops up right after I hit next on the agree to terms of use part. Anyone know how to resolve this? It only came with one disk, is there suppose to be another one and I just got jipped? Sorry if this is in the wrong area.

Thanks in advance to anyone who replies.

Update: I Just noticed the disk says ROME total war Barbarian invasion. It doesn't say barbarian invasion on the box. Is this a mix up?

The disks Says Rome Total War: Barbarian Invasion, which requires Rome Total War to install. You bought the expansion without the main game.