So, go to the Virtual Servers section of the DIR-655's Advanced tab. Create an entry called Wake-On-LAN-9 (just to be descriptive, the actual name doesn't matter, call it Bob if you like). Assuming you use the subnet 192.168.0.xxx, specify 192.168.0.255 as the IP address. Set the public and private port to 9 and the port type to UDP. Make sure you put a checkmark in the checkbox to the left and the click Save Settings.
If you want to use port 7 instead, substitute 7 for 9 in the above description. I use 9 because that's what the WOL tool at BroadbandReports uses.
Also be sure to have enabled WOL in the properties of your network adapter. For Windows 7, go to ControlPanel->NetworkandInternet->NetworkandSharingCenter->ChangeAdapterSettings. Right click the icon for the primary network adapter and choose Properties. Click the Configure button. Select the PowerManagement tab and make sure there are checkmarks next to "Allow this device to wake the computer" and "Only allow a magic packet to wake the computer".
Then be sure that PC is sleeping and not totally off (although some systems support waking from a totally-off state, check your BIOS for such a setting if you want/need to do that).
Then use your web-based tool of choice to send the WOL signal to your public IP address (check what it is at whatismyip.com if you don't already know how to figure it out), specifying the MAC address of the PC that you want to wake up. You can determine that from the list of DHCP clients on the Network Setup section of the DIR-655's Setup tab. Or if it is a Windows box, just use ipconfig /all from a command prompt and copy down the value it lists for physical address of the primary network adapter.
This works fine for me with my DIR-655 A3 with FW 1.33NA.
If it is not working it can be helpful to turn on every type of log message on the Logs section of the DIR-655's Status tab. Send the WOL signal and if it does not work, check the logs to see if it was received or not, possibly blocked, etc. and take corrective action based on what you find. Do the same for any software firewall you might be running.
Best of luck to you.