Re: My AMD system is very laggy on Ubuntu 13.10
You need to remove the non-free ATI driver if you have installed it. It wontbwork with your old graphics card. Only the default, open-source one will work, albeit with low performance.
Unity can be sped up by turning off animations and semitransparency which causes most of the speed problems you notice on that old video card. Do a Google search, it is easy to turn off the animations and transparency and it makes a real difference on old ATI cards.
If you can't find the instructions on Google, PM me and I'll find the instructions for you from my archive.
I try to treat the cause, not the symptom. I avoid the terminal in instructions, unless it's easier or necessary. My instructions will work within the Ubuntu system, instead of breaking or subverting it. Those are the three guarantees to the helpee.