Ernie2, that is very clear, which is just what we need, but are you absolutely sure of what you say - have you tried clean installs from scratch to test this?

Its just that, from inspection of th4 source code, it does look like I have hardwired "Program Files" as the installation folder, but I haven't made the mistake of always looking for texture packs there.

I've tried installing glidos on two rather different german (not messed-up)
XP systems and they both pointed by default to Program Files. As Ernie
said this directory does not exist, but that's not the point with hardcoded
directory strings.
Installing went fine, it just created automatically the Program Files directory,
just tried it again.

I was going to say Paul that Ernie2's long explanation seems to suggest an error in where Gilods looks for texture packs, but if you've checked and there ain't one, it seems rather bizarre!

Exactly. I certainly cannot find any hardcoding of "Program Files" other than in the installer. I rely on the "current folder", which should be the one from which the exe was loaded. I can't really see how Windows could mess with that.