Doesn anyone know how to do this? I' ve tried to find a tutorial, and can't find a decent one anywhere.

Go to Image >> Adjustments >> Desaturate. :)

Yeah, that works.
You can also do a greyscale. If you have PSP7, 8, or PSP9, then just click
Image>>> Greyscale
And if you want to use brushes on it that have colors, make sure you click
Image>>> Increase Color Depth>>> 16 million colors

:)