Well, not sure it will work for everyone, but on my dual core here is how i managed to host a game.
1 Start "Dedicated Gameserver" from the start menu->GOG.com->Sacred Gold (as Ois suggested in post #4)
2 Choose a name, keep default port and choose "LAN"
3 You can change game type from the "Game Configuration" menu
4 Launch Sacred Gold
5 Choose Multiplayer
6 Select your character, click next
7 Now you should see the game name you choosed on the server, JOIN it
8 Other players should be able to join too
If i try to host a new game from within Sacred, Gameserver.exe doesn't seem to load properly. At least it doesn't show in Process Explorer. I didn't try messing with cores so far as this trick seems to work.
And i kept network latency to DSL/Cable/LAN so that useless NPCs are not removed and i can see children run away from my demoness :D
EDIT: I'm an idiot. Forgot about the ISDN setting. However I'm using a quad core Windows Vista 64 bit and my friend is using windows 7 dual core, and we tried these methods listed on Hamachi, but still no go. Speaking of Hamachi, I can't find any help on google for Sacred Gold...just Sacred 2.