XSL Get Distinct Node Count

I have an XML document that looks like this:

<NewDataSet>
<Table>
<Column1ID>1</Column1ID>
<Column1>Movies</Column1>
<Column2ID>10</Column2ID>
<Column2>Mr. Deeds</Column2>
<Column3ID>20</Column3ID>
<Column3>DVD</Column3>
</Table>
<Table>
<Column1ID>1</Column1ID>
<Column1>Movies</Column1>
<Column2ID>12</Column2ID>
<Column2>Terminator 2</Column2>
<Column3ID>20</Column3ID>
<Column3>DVD</Column3>
</Table>
<Table>
<Column1ID>2</Column1ID>
<Column1>Music</Column1>
<Column2ID>13</Column2ID>
<Column2>Metallica</Column2>
<Column3ID>22</Column3ID>
<Column3>CD</Column3>
</Table>
</NewDataSet>

I am trying to build a Treeview out of this xml using XSL. What I want to be able to do is get a distinct count of Column1ID. For the XML provided I would have a total count of 2 (Movies & Music).

Does anyone know how I can accomplish this?

TIA!

Shaggy