After reading this forum for the past couple of months, I finally got WOL to work over the internet. The solution is talked about here:
http://forums.dlink.com/index.php?topic=5934.0
Although this solution did not work for me the first time. I tried the different subnet masks (255.255.255.128 and 255.255.255.0). It was only after reading this thread that I realized that there was a preset Wake-On-Lan in the Virtual Server Application Name List (the last drop down item). I discovered that it was important to use the preset Wake-On-Lan to make this work. Prior to this, I had created my own "WOL", which was unsuccessful.
I am using subnet mask 255.255.255.0 and used the "trick" of disabling JavaScript in Firefox in order to save 192.168.0.255 as a valid Wake-On-Lan IP address.
So...the preset Wake-On-Lan was the key for me to making WOL to work over the internet.