Hey if anyone has been getting the blackscreen while trying to load the game, here's the fix I did.

Basically I had to go to the C:\Program Files\Activision\Call of Duty - World at War\main\video folder and delete everything there.

I go into a little more detail about it on the website here:
http://truthae.blogspot.com/2009/06/black-screen-in-call-of-duty-world-at.html