I\'m almost positive this has been answered already; however, unable to find it since XY coordinates are overloaded due to their relative definition.
What I am tryi
I believe you are looking for something like the Mercator projection.
Somewhat related, but going the opposite direction: http://answers.yahoo.com/question/index?qid=20080521142713AAnlVtI
Also filled with information: http://msdn.microsoft.com/en-us/library/bb259689.aspx