Let's say I got this computer, and bought an ati radeon 5750 from fry's.
Would it be easy to replace that 9100?
Should work.. ask at frys, they'll know more about that motherboard/case than we do... but as far as i can see it shouldn't be a problem.
Also if i'm right you can't replace the 9100 as such because it's not discrete (it's integrated)
On the other hand that unit doesn't seem great value for money, when compared to building yourself.. but if your mind is made up i guess i can't change that.
Just remember that unit only comes with a 300w PSU.. and the time your saving by buying a unit instead of building it will likely be spent changing out that crappy PSU in a years time anyway