Question about recently bought ATI Radeon 5450

[bbqz986]

Hi! I have just recently bought a new computer, with the following specs:
Intel i5 CPU 750 2.66GHz, Kingston 4GB DDR3 1333Mhz, and a ATI Radeon 5450 1GB 3MSI.
The OP is Windows 7 Ultimate 32 bit.
I have a Samsung "SyncMaster 931BF" screen, wich allows only the maximum resolution of 1280X1024.
From what I know, this computer should be able to run most new games on High quality on this resolution.

The problem is that in any game I install I encounter the problem that... well....
NONE of the games work without lagging when they are set onto High quality.
I am talking about games like Assassins Creed II, Just Cause II, GTA IV, Bioshcok 2, Crysis, COD:MW2
etc.

I have noticed that when I adjust the settings in the ATI control center, from Performance to Quality,
the Quality is great, but the game is horribly lagging. When I adjust in from Quality for performance,
the games look just HORRIBLE.

I would like to ask for your help in adjusting the graphics in the right way in the control center..
or any of the solutions you can offer.

Thanks in advance!

Daniel Bas.