Merge multiple .pst (MS Outlook) files

Note -- this is one of two threads with the following titles:

   • Merge multiple .pst (MS Outlook) files
   • Remove duplicate email messages from merged .pst (MS Outlook) files.

Hello,

Does anyone know of an easy way, or some easy-to-use software that will merge multiple .pst files?

I have been using Outlook for many years and during that time I have had a few different computers and a few different external hard drives (which I still have) and numerous different saved .pst files on those hard drives.  Knowing that they contain certain items which I want to save, I have always just stuck them in some folder with the thought that I would get back to them at some point to filter out all the other stuff.  However, despite the years which have transpired, I am still no less confused about .pst files than I was then!  

Therefore, I am hoping that there are enough other people with similar circumstances, that someone, at some point, has developed a really awesome way to do just what I am inquiring about.  If anyone is aware of something like that, I would be very happy (and appreciative) to hear about it.

Thanks