I have a 27" Viewsonic 1080p monitor connected to an oldish Mac Pro with an ATI Radeon X1900 XT Graphics card. The problem is that the image does not fill the screen?!?!?

I know the image can fill the monitor, because at start up, the white Apple logo screen fills it up. But once the system starts up, there are bands of black framing the image. I have searched extensively on the internet and found the following clues, none of which solved the problem:

1) In the Windows world you can get software from ATI called Catalyst Converter that gives you the cpaobility to scale the image. This software/feature is not available for Mac users.

2) Viewsonic's web site has a trouble shooting tool. This came up in response to the topic "you have recently upgraded to a larger monitor"

"This could be an issue if you have an older Apple using the system's onboard memory to support both the system and video display. Even if you have enough onboard RAM to support a higher resolution, it will not since the system will use some of the memory. Because the true video RAM available is much smaller than the total onboard amount, the system limits the size of the image. You will need to contact Apple to get an upgrade in onboard RAM or update the complete system."

I have 2GB of RAM, so lack of RAM memory does not seem to be an issue. I am running OS 10.6.8

Does anyone have any clue how to solve this problem. It is frustrating to have a 27" monitor behaving like a 25" monitor.

Thanks in advance for sharing any experience on this.

JD in PA