I figured it out
I ended up using Delay's blog.

http://blogs.msdn.com/b/delay/archiv...-charting.aspx

The only thing I did a little bit different is after you take the default template off here:

http://silverlight.codeplex.com/Sour...w/18791#507649

Stick the whole thing in the

<Application.Resources>

</Application.Resources>

section of the app.xaml page. but you need to give it a name. Change line

<Style TargetType="charting:LineDataPoint"> in the defualt template to something like this

<Style x:Key="MyLineDataPointStyle"

So when you put this:

<charting:Chart
Title="Custom ToolTip">
<charting:ColumnSeries
ItemsSource="{Binding}"
DependentValueBinding="{Binding Length}"
IndependentValueBinding="{Binding}"
DataPointStyle="{StaticResource MyColumnDataPointStyle}"/>
</charting:Chart>

On your mainpage.xaml The datapointstyle has something to reference. Now you can change the
tool tip on the app.xaml page to anything your heart desires.