Hi Sebastian,
Sorry, I don't have the faintest clue about the wifi usb adapter method.
My setup is as follows. Motherboard Asus p4S800-mx (I know it's old, lol); linksys WRT54G router (old as well :P); Linksys (LNE100TX) EtherFast 10/100Mbps LAN Card with WOL. I've only done it on a local wireless network but I read a certain
Liam Wesley was able to make it work on a WRT54G router using broadband and port forwarding. I have yet to try it though.