Btw if you enable DMZ you dont have to mess around wiht any port settings but you are put outside the routers firewall (if your router has one, and if its turned on) Also if DMZ is on you are basically usiong a straight connection to the internet again but you will have no security but you will be running of a routers i.p. address which is supposidly unknown to hackers but thats crap lol trust me anyway if you have a anti virus with latest definistions with or without a firewall of any security if anything gets in your pc then it wont go anywhere, the anti virus will detect and destroy it instantly.

@Elkwyn, the information about routers reflects on your problem too as you said your using one also, (btw this is irrelivant but if you dont know anything about routers this is espeically to wireless router users, then your connection is most probably not encrypted and any body can gain access to web through your service lol for free, just thought id let ya know ^^)

To get up a list of blocked/permitted/semi permitted items double click on your little icon for the firewall should be greeny ball thingy lol in bottom right of pc screen, then when ya norton home firewall screen comes up go to personal firewall section tab on left of screen then 4 more sections inside there drop down and you should click on Internet Access Control in here is the full list of everything thats permitted and blocked etc you can delete things out of the list if you wish and if mtw or vi is in there id advice deleting them then next time you access the game a block pop up should come up and when it does hit permit and then tick in bottom left of the box always do same thing lol, btw many people dont check all the settings of there firewall to the left with all the sections, it pays too :)
Privacy Control is another main tab, in here you can set your information level, you home users may want to set it too medium it gives ou more info on game access for example when accessing them then on low, and it will pop up with permit/block option for more games

Anyway my minds gone blank now, so if any more help is needed ask, trust me its simple guys and your get there evntually.
Hope i was of help