Linux install ok, Windows install not ok (XUL app)

I'm writing a standalone Mozilla app with XUL & JS (i.e. it's not 
intended to be displayed in a browser). I wanted to see how it might 
work in distribution so I packaged up the embryonic app into a .xpi file 
(win Winzip on a PC), and used mozilla to install it on both Linux and 
Win2K systems.

On both systems the app is invoked with the command line argument:
-chrome chrome://etgconfig/content

This runs the app just fine on Linux, but on Windows I only get an alert 
box with the message "The file /content/etgconfig.xul cannot be found. 
Please check the location and try again." The install put the etgconfig 
directory tree under chrome/ and added entries to installed-chrome.txt. 
As far as I can tell moz did the same thing on both systems, but I can't 
run my app on the Win2K system. What am I doing wrong?

I've copied the install.js file below if that's of any use; the contents 
of the .xpi file are as follows. (The .css file will eventually move to 
a skin dir, but I'm just experimenting now.)

install.js
etgconfig/content/etgconfig/contents.rdf
etgconfig/content/etgconfig/etgconfig.css
etgconfig/content/etgconfig/etgconfig.js
etgconfig/content/etgconfig/etgconfig.xul
etgconfig/locale/en-US/etgconfig/contents.rdf
etgconfig/locale/en-US/etgconfig/etgconfig.dtd

install.js:

initInstall("ETG Config","/Symmetry/ETGConfig","0.1.0.0");
instDir = getFolder("Chrome","etgconfig");
setPackageFolder(instDir);
addDirectory("etgconfig");
registerChrome(Install.CONTENT | Install.DELAYED_CHROME, 
getFolder(instDir, "content"));
registerChrome(Install.LOCALE | Install.DELAYED_CHROME, 
getFolder(instDir, "locale"));
performInstall();