How do I make non-iTunes files appear in the iTunes library window?

You can’t just add stuff to the iTunes folder. There is a command in the menus for either adding an individual file or adding an entire folder. You need to use these to add music to iTunes.
There is a setting in the preferences that controls wether or not iTunes leaves the files where they were or copies them into the iTunes folder.

What is the format of the files? iTunes only supports files that play in QuickTime. If you have a avi file you will need to convert them first.

You don’t just copy files into the iTunes library directories on your computer.

See, the way it works is that you use your mouse to drag your media files into the Library area of an open iTunes application window. iTunes will then copy the files from their original locations over into the iTunes Library directories (unless you have it config’d to leave them in place). Once that copy operation is complete, iTunes then updates its database with information about those files, like where they are, what kind of star rating you gave them, when they were added, last played, etc.

The iTunes application window is showing you what it has in its database which, as you’ve discovered, is not just a plain old directory listing.

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You should treat the iTunes library directories as a read-only source… meaning that if you want to grab a copy of some song or movie, you can find it in there and copy it out if you want. But you should avoid making any modifications to the files or structure of the iTunes library directories as that will put them out of sync with where iTunes expects to find them (as mapped in its own database.)

In your music folder iTunes creates a folder called Automatically Add to iTunes.

Put the files in there and iTunes takes care of things from there.

Wow, lookitthat: C:\Users\ (userid) \Music\iTunes\iTunes Media\Automatically Add to iTunes

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I just lurve learning new things on Fluther. Thanks, @jaytkay!