Vista - Bitmaps with transparent background in WPF

Hello,

I'm doing my first steps with WPF and I want to create a ToolBar in XAML
like this.

<ToolBarTray DockPanel.Dock="Top" >
<ToolBar Band="1" BandIndex="1">
<Button><Image Source="Resources\NewDocumentHS.BMP"/></Button>
<Button><Image Source="Resources\GoToParentFolder.bmp"/></Button>
<Separator/>
....
</ToolBar>
</ToolBarTray>

For the bitmaps I want to take the images from
C:\Program Files\Microsoft Visual Studio
8\Common7\VS2005ImageLibrary\bitmaps\commands\16color
C:\Program Files\Microsoft Visual Studio
8\Common7\VS2005ImageLibrary\bitmaps\commands\24bitcolor
C:\Program Files\Microsoft Visual Studio
8\Common7\VS2005ImageLibrary\bitmaps\commands\32bitcolor

How can I paint the images without the background color.

If I'm using the PNG images the tollbar will be bigger and the images are a
little bit out of Focus.

Ralf