Download the AS3 code which will correctly calculate the x/y coordinates from latitude and longitude.  
You can see the code is correct if you compare the values it outputs to those found at http://spatialreference.org/ref/esri/54030/when using the actual earth’s radius in my code (see comments in code).  

The exact value of the x/y coordinates however depends on how the map has been scaled.
If you take the globe and project it into X/Y coordinates it will have a maximum width that is 1.97165551906973 times the maximum height.  To get the projection to work, you need to make sure that the map you start out with has a width that is 1.97165551906973 times greater than the height. From my rough calculations, the original Wikipedia map (http://en.wikipedia.org/wiki/File:BlankMap-World6.svg) fits these dimensions when you crop off the extra whitespace carefully.  

Once you have this map, take the width of the map and divide it by 2.666269758.  Take the height of the map and divide it by 1.3523.  You should get the same number either way if you did part 1 right.  Take the number you just got and divide it by 2.  Replace the earth radius variable in the AS3 file with this last number (found right after latitude and long inputs).

Now the AS3 file will give you the correct X/Y coordinates when you input latitude and longitude.  These X|Y coordinates will be based on an origin (0,0) that is located in the absolute center of the map near Western Africa.  You need to adjust them so that they work with Flash's origin that is located in the upper left hand corner.  This adjustment should be done by taking the x value and adding one half of the maps pixel width.  Also, take the one half of the maps height and subtract the y value to get the correct y value.

At this point you will also need to make any adjustments if you added extra spacing to the map.  Please try some lat/long's for cities that you can eyeball on the map (like Miami or Cape Town, South Africa) and calibrate the map accordingly.