I have upgraded this model {z5771} all in one...... and it was easy,
google up the service manual{z5771}.....that will show you how to remove the back cover,
I have ran a gt 520{2gb} and now have a gt 530{2gb} and have encountered no problems at all,
I did not even have to upgrade the power {135 watts}
I have played games like total war {empire, mtw2,napoleon} without any problems or cut outs
the gt 530 plays games better than the gt 520 because it has a better memory width.......
but yeah just to let people know it can be done and it is a good upgrade for these machines,
what I will say is though...once you remove the back cover ..the warranty will be void.....
cheers