File store organisation

I'm looking for a setup that allows me to arrange the files so that each can be placed in to multiple "directories" - maybe some form of categorisation or tagging? Maybe I'm looking to define (searchable) metadata for the files?

Tabbles does that and a lot more, check out the various links under the "What is it?" menu.

The mechanism you might be looking for is maybe "Libraries", introduced in Windows 7.

See this lifehacker introduction, Get to Know Windows 7 Libraries Inside and Out :

The new Libraries feature in Windows 7 makes it easier to manage your files and folders. Today we take a comprehensive look at everything you can do with Windows 7 Libraries.

The Libraries feature in Windows 7 provides a central place to manage files that are located in multiple locations throughout your computer. Instead of clicking through a bunch of directories to find the files you need, including them in a library makes for quicker access.

Microsoft makes available this introductory video: Organizing with Windows 7 Libraries, as well as this article.

This article may also be useful Windows 7 Libraries Explained – And Why You Want Them :

Windows 7 contains a set of libraries. Each one works that same way, and they all take the place of the standard folders in XP and Vista.

A Library can be treated like a folder with a group of subfolders inside it, and can also pull some nifty tricks all of its own. The important thing to remember is this: the subfolders are not actually stored in the library. They are just made to seem as though they are. Each library has some default contents, but you can change these, and also create new libraries if you wish.

I'm looking for a setup that allows me to arrange the files so that each can be placed in to multiple "directories"

Hardlinks. If you're using a directory hierarchy to organize your files, you can continue to use it. Just put the file itself into multiple directories, but use hardlinks so you're actually only storing the file once. Link Shell Extension will make creating the links themselves easy to do.

Most backup software should be able to handle hardlinks or symlinks without issue. LSE makes tracking down all instances of a multiply linked file little more than a property sheet away.