Dungeon Siege II on LAN with XP no go ?

Just a question for all the game pros:

I try to set up a lan connection with an XP (SP3) machine which worked just fine when I had Vista. We get as far as that: No matter who hosts, the other one just can't join (meaning you click JOIN and nothing happens)
Firewalls are opened, we can ping each other just fine, Update Patch to v2.2 went through and I even ran regsvr32 dpnet.dll successfully. Both machines hang on Ethernet ports of my Wifi Router (Cisco Lansys) but that didn't change since I tossed out Vista and made a clean install of W7.
What am I overlooking here?

-DG

Is there a connect by IP address in the game? Can you both see each other in the Windows Explorer when you look through your network?

Thanks for trying, halo200.
But sorry, it's not like Diablo where you can enter alocal IP to connect to. As a matter of fact I don't believe it's a connection issue at all: both computers are completely "networked".
I even have some partitions of the XP as Network locations in W7. The other way around, the XP displays movies streamed from my external USB drives which are connected to the Windows 7 machine.

Like I said the whole setup hasn't changed except for me switching from Vista to W7.
I guess the ultimate question is how gets W7 handled differently fom the way it's handled in Vista by DS II.

-DG