Actually, I have already released a freeware few weeks back which helps the user to obtain the black bars (other colors for "flat" bars not available though) in WM5. This would be pretty convenient rather than keep using the "special" TSK/CABs which contain the registry tweaks. More info on the application can be found here. The discussion and suggestion/development thread is found here.
It's as simple as ticking "Use black bars" to get pure black bars on your WM5 device.