[MrJackdaw]

Assuming the window is called "Window" and the place you want to store the data is a table called "Data";

Window.PositionChanged=function(sender,args)
	Data.x,Data.y=Window:GetPosition()
end

Will store the window position to the Data table whenever the window is moved.

Then, when you load the data - just use the Data.x and Data.y to load in the position.

Assumption: You are saving the data at some point with;

Turbine.PluginData.Save( Turbine.DataScope.Character, "The Name of Your Plugin", Data );

And loading it with;

Data=Turbine.PluginData.Load( Turbine.DataScope.Character, "The Name of Your Plugin")

or similar!