http://technet.microsoft.com/en-us/sysinternals/bb896653.aspx

Process Explorer v11.33 By Mark Russinovich
Published: February 4, 2009
Introduction

Ever wondered which program has a particular file or directory open? Now you can find out. Process Explorer shows you information about which handles and DLLs processes have opened or loaded.
* if Process Explorer is in DLL mode you'll see the DLLs and memory-mapped files that the process has loaded. Process Explorer also has a powerful search capability that will quickly show you which processes have particular handles opened or DLLs loaded.

The unique capabilities of Process Explorer make it useful for tracking down DLL-version problems or handle leaks, and provide insight into the way Windows and applications work.
http://technet.microsoft.com/en-us/sysinternals/bb896645.aspx

autorun

http://www.diamondcs.com.au/ * most are free

ASViewer allows you to instantly view over 50 different autostart locations to check (and have complete control over) which programs are starting automatically when Windows starts.

all are free and work on windows 98 to windows 7

This could be your cup of tea (so to speak): http://www.dependencywalker.com/

The F.A.Q. is here: http://www.dependencywalker.com/faq.html

I also found this command line trick: How to See What DLL Files are used by Programs

Hope this helps

Quantum Dragon AKA Paul

Thanks GMMan for your suggestion, but it's not really what I'm looking for.

Digging back in my memory, I think the program came bundled with an old anti-virus program (can't remember which one now), but I now recall that it was when you chose "Properties", there was an extra tab to display all associated files.

It's a bugger getting old . . .

Hmm... I don't have exactly the right program, but the closest I know is TrID. You can put it in your Program Files, install some definitions, and make a custom items so that when you click on it it feeds the program into TrID and tells you what the file is most likely to be.

Not so much a suggestion, but also a request.

I would really like to find a program (free or otherwise) that allows you to right click a file in Explorer or My Computer that from the context menu allows you to see what programs use that file, and vice versa.

For instance, check an DLL file to see what installed programs use it. Also, check an EXE file to se what files are needed for that program to run.

I did have that facility many years ago on a very old computer, but I have forgotten what program it was that achieved it.

Cheers,
Postyr