I'm running Win7 on a 64 bit machince.

If you install and older verision of Direct X, does that mean you have to install the newer version again if you want to play newer games?

No, for DX9 and after they are all standalone, and can run side by side without interferring with each other.

I do not believe so.

For all DirectX 1 to 9, the following applies:
- Installing any of these DirectX versions will update your files if the files in the installer are of a more recent version than those on your machine
- If the DirectX installer notices that its files are older than the ones you already have installed, it will skip them, it won't overwrite your newer files with its outdated ones
- Newer versions of DirectX are backwards compatible to older ones

This means: If you have the latest version of DirectX (which is currently DirectX 9.0c from June 2010, if I'm not mistaken), you don't need to install any older versions to make older games work, but _if_ a game runs an installer for an older DirectX version, it won't do any harm either.

The situation is slightly different for DirectX 10 (which came with Windows Vista) and DirectX 11 (which came with Windows 7). Those versions are _not_ backwards compatible, and they do not replace older versions of DirectX.

Since you have Windows 7, you should install:
- DirectX 11, for the newer games
- DirectX 9.0c from June 2010, for older games

Once you have those two installed, you don't have to worry about DirectX anymore.

^ Nope.

What the DirectX redistributable package installs is not the core of DirectX (like the most important things to run DirectX games), but optional files through which Microsoft have provided additional features (or alternative ways of doing things) based on developers' request.

The actual DirectX can only be installed through a service pack or a major Windows update.

It doesn't matter if a user installs the package released in 2010 or the one released in 2006 (of course, we're talking about files located in both versions of the package). The files are NOT outdated since they don't get updated once initially released.

Regarding this user, and pretty much every other 7 user, they already have DX9, DX10, DX10.1 and DX11 installed, but don't have installed the optional files (which usually become obsolete once a major version of DirectX has been released, but heh, games don't really change DX requirements so we have to install these optional files no matter what core DX our OS comes with).

You're talking semantics (which, to be honest, is going to confuse the average user more than help them). 99% of users assume that the package which gets installed by games, or can be downloaded from Microsoft, which is called DirectX on both occasions, _is_ DirectX. You can of course tell them that in fact it's just additional files that are adding to a core which is already present, but what's the use? It's an unnecessary detail. Well, since most DirectX 9 games _don't_ run on Windows 7 without installing the package, and _do_ run after installing it, I'd say that it matters quite a bit.

You're correct in stating that the individual files don't actually get updated, the package just gets expanded by additional files. But, again, the practical relevance of this difference is zilch, since it doesn't change the recommended course of action.