Google for GAG boot manager and install it on your computer. It will hide the vista operating system so that you can install the XP as if it was the only operating system installed...it will then allow you to use the dual boot proccess.

This is the easiest and simplest way to dual boot. you will need to have all the needed xp drivers for your hardware configurations go to Acer's website and look for the xp driver files for your model!