Question driving external LCD from dell laptop

[geisj at pagestation.com (Jerry Geis)]

I have a dell inspiron 8200 laptop running centos 4.1 just fine.
I want to connect it to an external 32 inch LCD.  This laptop is dual 
boot windows.
I set windows up to 1024x768 and connected the LCD - it worked just 
fine. LCD max is 1333x768

I then booted Centos 4.1 and set X to be 1024x768 also. rebooted the 
laptop just ot make sure.
I then connected the LCD and it says can't display it...

Any ideas on how I might get the LCD to display CentOS X?

Thanks,

Jerry