Only Counter Strike works! Help!

I am having problems with LAN games not based on the quake 2-3 engine. I am able to play multiplayer games such as Counter - Strike (Quake 2 engine) and quake 3 with no problem. They connect like they should and they dont lag too bad.
The problem is when I try to play games like Unreal Tourny and Tribes 2 over a LAN. The game lobby deal doesnt see any games and whenever I host, no one else can see the game. All my network settings are optimal and working, but those games just dont work. Tribes 2 does work when I try to play over the internet. Any help you guys can get would be appreciated, thanks in advance.

My system:
T-Bird 1.2@1.4 GHZ
256 MB Micron PC133 2-2-2 RAM
Iwill kk266 mobo
D-Link 10/100 Network card.
Radeon 64 MB DDR VIVO
US Robotics 56 K Hardware Modem
Windows 98 SE