what is the desktop resolution set to in system preferences?
After catalyst starts - what does the catalyst control window show as the resolutions on each screen?
I'ts possible that you might have a setting enabled in catalyst that is reducing the screen resolution.
You mention that your content is from a 'lot of different sources'...
I'm sure that it must be royalty free - or you own the copyright / licence... ?
Do check the codecs and resolutions of your content - if it is internet sourced - this may explain the problem...
Do get back to me if you need some more help
S