There is a hidden feature in the latest update from Apple. You can use Safari to test dashboard widgets via the hidden debug menu:

Friday’s update of Mac OS X 10.3 to version 10.3.9 included a few unmentioned surprises, Safari 1.3 and new versions of WebKit, WebCore, and JavaScriptCore that “contain thousands of improvements… made to the engine since Safari 1.2.” In addition to what Safari developer Dave Hyatt says is a 35% speed increase, the update includes a feature geared towards Widget developers, the “Use Transparent Window” option. The option, which can be found in the hidden “Debug” menu, allows you to preview widgets in an environment more visually similar to Dashboard, in a transparent layer over the desktop.


To enable the Debug menu, quit Safari and enter the following command in Terminal:


% defaults write com.apple.Safari IncludeDebugMenu 1

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I haven't given this a try. But why don't you try it and report back?

Zefi

tried it last night.
works well but you still dont get full dashboard functionality.
but its good for testing layout stuff.