Unfortunately, this proved to be a BIG MISTAKE!

Moments after installing the software, all my new shell windows reported that mkdir, doskey, ipconfig and even HELP are 'unrecognized' - so began my hour-long search for a resolution to the amnesia that had suddenly afflicted the command-line.

The problem turned out to be two-fold:

1. It would seem the installation script (setup_xampp.bat) or shell script (xampp_shell.bat) had a misunderstanding with some of my custom command-line settings. In fact, it decided my PATH environment variable wasn't up to scratch... so it erased it! This meant that the command-line had no idea where to look for system apps. and as result shut-down a large portion of my system utilities.
2. In addition to the above, the script added to my default shell script (HKEY_USERS\...\Software\Microsoft\Command Processor\AutoRun) a small 'set PATH=' command that each time it was run added the XAMPP directory to PATH and then deformed it with an increasingly long string of semi-colons.

Needless to say, I'm somewhat annoyed that there is no visible warning during installation that it could potentially FUBAR your environment variables. I hope this provides some insight for people who might be experiencing a similar problem.