I did the build on MacOS 10.5.0, but I think I have things set up so that it will all still run on 10.4.0 or newer.
However, early reports indicate that the Dashboard widget doesn't work on 10.4.10. Update: Fixed! Re-download it. Version number unchanged.
Also I signed the code with a self-signed cert. I wonder if that did anything sane. It's surprising that signatures don't show up in Get Info in Finder.
Dashcode is weird. I couldn't figure out whether I should check the .wdgt into CVS or the .wdgtproj or both.
Also I couldn't figure out how to make the widget be resizable, or how to add color selectors to the preferences panel on the back.