If you notice that the Presenter '09 icons that appear on the Articulate tab in PowerPoint 2007 don't have a transparent background, your display color settings are likely set to 16-bit Colors. You can correct this by setting your display settings to 32-bit.
To set your display color settings to 32-bit:
Right-click on your desktop and select Personalize
In the Colors drop-down select Highest (32-bit)
The Articulate Presenter '09 icons should now appear correctly.