Refactoring "include file hell"

One thing that's really been making life difficult in getting up to speed on the codebase on an ASP classic project is that the include file situation is kind of a mess. I sometimes find the function I was looking for being included in an include file that is totally unrelated. Does anyone have any advice on how to refactor this such that one can more easily tell where a function is if they need to find it?

EDIT: One thing I forgot to ask: does vbscript have any kind of mechanism for preventing a file from being included twice? Sorta like #ifndef's from C?

There are a few basic things you can do when taking over a classic ASP application, but you will probably end up regretting doing them.

1. Eliminate duplicate include files. Every classic ASP app I've ever seen has had 5 "login.asp" pages and 7 "datepicker.js" files and so forth. Hunt down and remove all the duplicates, and then change references in the rest of the app as necessary. Be careful to do a diff check on each file as you remove it - often the duplicated files have slight differences because the original author copied it and then changed just the copy. This is a great thing for Evolution, but not so much for code.
2. Create a rational folder structure and move all the files into it. This one is obvious, but it's the one you will most regret doing. Whether the links in the application are relative or absolute, you'll have to change most of them.
3. Combine all of your include files into one big file. You can then re-order all the functions logically and break them up into separate, sensibly-named files. You'll then have to go through the app page by page and figure out what the include statements on each page need to be (or stick with the one file, and just include it on every page - I can't remember whether or not that's a good idea in ASP). I can't comprehend the pain level involved here, and that's assuming that the existing include files don't make heavy use of same-named globals.

I wouldn't do any of this. To paraphrase Steve Yegge (I think), "there's nothing wrong with a classic ASP application that can't be fixed with a total rewrite". I'm very serious about this - I don't think there's a bigger waste of a programmer's time in this world than maintaining an ASP app, and the problem just gets worse as ASP gets more and more out of date.