Connection problems

[Leyawin]

I have lately been trying to play a few games where you must connect to your opponenets IP adress or he must connect to yours. However, i am never able to connect, even though he and me have the correct Ip adress. I tried it with other people, and it still didnt work. This problem occurs on all games based like that, and its really ticking me off. An example of a game that doesnt work for me is little fighters 2, as well as yu-gi-oh virtual desktop (YVD). Also, when i try to host a game on "Paintball 3 Extreme"" it still doesnt work. just ignore the wierd games i just wanna no how to fix this. my dad is running a Vshield filter as well as a viruscan console. Im using firefox if that helps at all. Im running a comcast cable internet connection, and using a windows 2000.