Yup, I've got that. If you have a clean copy of Rome Total War (or EB 1.1), you simply copy that folder twice and install EB 1.2 into one of them, and WotB in the other. The third you keep for other mods or modified versions of EB (like I have one for WotB, one for BtSH, one for single, one for MP + backup and one for the PBeM).
If you don't have a clean copy of RTW or EB 1.1, I'm afraid to do it you would have to reinstall it. You wouldn't lose your campaign (get it out of its folder*, like to the desktop or whatever to keep it), but it is a bit of a hassle. Me, I love installing/updating things, so I don't mind doing things like that, but from what I hear most people find it dull. I guess I'm just crazy that way.
Edit: Damn my damaged Swedish-English alternation! Every time I intend to write folder I write "map" because the Swedish word for it is "mapp"! It's driving me nuttier!
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