Help with ports

[maumastoks]

Now I need help with ports.
Why? To be able to host a match on Touhou 10.5 Scarlet Weather Rhapsody game.

Now the whole thing:
There is no router.
My internet connection goes like this:
Cable -> Modem -> Desktop's Windows Firewall -> Desktop (XP) -> Wireless home network -> My laptop's F-Secure Client Security firewall -> My laptop (Vista).

What I tried:
1. Opened a port in desktop's firewall just by "Add port..." Didn't work (my F-Secure firewall in laptop has the Touhou program in allowed list)
2. Disabled my F-Secure firewall (Windows Firewall in my Laptop is always disabled). The port was opened in desktop. Didn't work.
3. Disabled both firewalls (desktop Windows Firewall and my laptop's F-Secure Client Security Firewall). Didn't work. The problem is not within the firewalls.
4. Installed the game to desktop and tried playing. It works with firewall. The problem might be with the wireless.

Modem is:

Motorola
SB5100E
SURFboard
Cabel Modem

Wireless is:

SMC
EZ Connect 2.4GHz Wireless
Ethernet Adapter SMC2671W

I tried opening a port in desktop's firewall for uTorrent too. Does not work either. So the problem is not within the game.

Any ideas what to do? Feel free to ask questions, I'll answer.

[Greg]

Your ISP could be blocking those income ports.