Your CPU doesn't support PAE.
In computing, Physical Address Extension (PAE) is a feature to allow 32-bit x86 processors to access a physical address space (including random access memory and memory mapped devices) larger than 4 gigabytes. (wikipedia)
The easiest way to install ubuntu with unity is to download and burn the mini.iso, you can get 12.04 or one of the other mini.iso's here:
Boot from it and follow the instructions, choose the latest linux-generic (without PAE) kernel (if you're asked to choose one, this depends on the choice you make how to install), and choose ubuntu-desktop when you are asked to select software to install. Do choose a desktop, if you don't you'll end up with a command-line system without a gui.
You might also consider to install Xubuntu or Lubuntu 12.10 because you are using an older laptop, Xubuntu or Lubuntu are more lightweight than Ubuntu and thus work faster. I recommend Lubuntu for speed.