W2K, long/short filename & Temp variable

On Win2000 when I open a DOS box and type SET sometimes the directory assignments for variables like TEMP and TMP are sometimes in long filename format and sometimes short filename format. I can’t seem to find a pattern to the display.

This creates a problem for installation of some older software. If long filenames are being used, the software can’t find the temporary directory and fails. But if W2K comes back with short filenames, the installation proceeds normally.

Anyone have a clue about this behavior? If so, is there a way to control it so that I can get the software installed consistently?