Different filename formats from Command$ function

I am using the Command$ function to obtain the path of a file when the user clicks on it.

On my usual laptop, running Win XP, the path is given in the Long Filename format eg "C:\Program Files\Common Files\myfilenamegoeshere.abcd"

However, when I run it on my other laptop, also a Win XP, I get the Short Filename format eg "C:\PROGRA~1\COMMON~1\MYFILE~2.ABC"

I am using four letter file extensions and the short form cuts this to three letters as above

Now, as it happens, there are Microsoft guides on how to swap between them as per:

http://support.microsoft.com/kb/175512
http://support.microsoft.com/kb/154822

but I really want to get to the heart of the problem rather than just kludge it. So, how can I force the Command$ function to return Long Filename format?

All help and comments appreciated
.