[TMXS]

But is it just the image files? Or the php files too? (although I don't see how that's possible)

Did you log into your admincp and look for the file paths? To make sure they're pointing to the right place?

Because of your forum's size you'll need to go through SSH to unpack it. If you've never done that before it'll be a bit difficult to get to where you need to be even with step by step instructions. You always have the option of overriding some of the folders and files, but if its as big of a mess as you say, you'll neet that clean install.