This sounds like a Windows Vista option and not an XP option.

In any case I have to ask the obvious question, how did you turn this feature on? Can you reverse your steps to turn it off?

Something like this will either be controlled by an icon in your System tray, (near the clock), or by right clicking an empty part of the Desktop and looking for anything to do with Acer GridVista.

You need to explore those and see how to turn the feature off.