zimlet to open website in main frame

[gregor]

hi,

how can i open a link in the main frame where the calendar or the task are shown?
the finale goal is to add a button after the settings which opens a website in the main frame.

i use these xml to test some ways

<zimlet name="com_zimbra_button" version="0.1" description="add a button to the main toolbar">
	<summary> These Zimlet add a button to the main toolbar after the preferences</summary>
	<zimletPanelItem label="text">
		<toolTipText>tooltipText</toolTipText>
	<contextMenu>
		<menuItem label="Open Website" id="www.yahoo.com">
			<canvas type="window" title="www.yahoo.com" width="800" height="600" />
			<actionUrl target="http://www.yahoo.com" />
		</menuItem>
	</contextMenu>
	</zimletPanelItem>
</zimlet>