"Run the executable file and direct it to your BG 2 directory. It should automatically start the mod setup."
Does it matter what # I input for the X Coordinate as long as it's higher than 641? Any random # will do? If so, what's the point of this step? Just curious.
I would set the X and Y coordinates to the native resolution of your monitor. This step determines what resolution BG 2 will be displayed at.
Let me put it another way. Check and see what resolution your system is currently using.
This Youtube video
covers how to change the resolution of your computer in Windows 8. Follow the steps and you'll see what the resolution is currently set to.
Once you know the current resolution of your system, enter that resolution into the widescreen mod.
The current resolution of my system is 1440 x 900.
I would enter 1440 as the X and 900 as the Y.
I hope that answers your question. Post if you run into any problems.