Developer Tools may be included on your Leopard Install DVD, if not it can be downloaded from http://developer.apple.com/tools/download/
If you have Leopard you would download Xcode 3.0
It is 1.1GB in size. Still interested?
With Developer Tools installed and working from your admin account:
Locate HD/Library/Widgets/World Clock
Make a copy of it and place the copy in Projects, or any where you want to save the copy to.
Back to the original, Select it and control click on it to find Open With, and select Dashcode.
First of all, save it as a different name with Save As; call it World Clockmod
Have the new location be Library (the default)
From the Toolbar select View (blue icon) and select Files.
Locate your language, English in your case.
Expand the folder to localizedStrings.js
In the right hand pane you will see various locaizedCitynames.
Locate the one you want to change.
eg.
localizedCityNames['Atlanta'] = 'Atlanta';
change the second instance to your local town name: eg
localizedCityNames['Atlanta'] = 'Newtown';
Make sure it is still in the 'quotes'
Save the file.
Quit Dashcode.
You will now observe the new file World Clockmod sitting at the bottom of the Library folder in the Finder window.
Double click on World Clockmod and you will be asked if you want to replace World Clock with World Clockmod. Say yes.
On the Dock click on dashboard, and position your new clock.
Select Manage dashboard to select it in the list if you want it to appear in the list of widgets.
