I think that I have a similar problem to a lot of the posts below, but I wanted to describe it to someone before I ordered parts. I have a Pismo 500FW that boots fine, but the screen is very dim - I would guess it is at maybe 5% brightness. I attached an external monitor and got the system preferences set to "mirror". The computer will run fine in this configuration for a few minutes, but then it will eventually freeze whatever applications are running. I can put a flashlight against the apple on the cover and it really helps the middle area of the screen.
What do you think my next step is? Is it the inverter board that I hear so much about - or is it something more than that?
Thanks for any replies.