I created this templated Silverlight CustomControl. Go ahead and download the source.
<Balloon:BalloonBox Grid.Row="1" Grid.Column="2" Type="MouseOverToShow" Grid.RowSpan="3" Grid.ColumnSpan="3">
<Balloon:BalloonBox.Header>
<TextBlock>Silverlight</TextBlock>
</Balloon:BalloonBox.Header>
<Balloon:BalloonBox.Content>
<TextBlock Width="185" TextWrapping="Wrap">Silverlight is a powerful development platform for creating engaging, interactive user experiences for Web, desktop, and mobile applications when online or offline.</TextBlock>
</Balloon:BalloonBox.Content>
</Balloon:BalloonBox>
BalloonTest.zip (69.43 kb)
Tags: silverlight, customcontrol, blend