OK, so I didnt find any thread like this on the forum, so I thought I should make one for the sake of everyone, including myself, as I cannot connect to more than one person at a time!
Below are all the problems you may have and how to fix them!
Port Forwarding
First of all, port forwarding is a tricky business. It requires a static IP and some router skills. No need to worry though, because your Internet Provider can probably walk you through all of the steps.
Also, if you don't want to learn how to do all this junk, try this out, it will automatically do it for you!
https://portforward.com/store/pfconfig.cgi <--- TRY THIS!!
Gotta pay for this one.. :(
Try this website for more info, I found it very helpful!
http://portforward.com/networking/staticip.htm <--- Click this first
Make sure you follow all the steps very carefully, otherwise it wont work!
http://portforward.com/routers.htm <--- Then this one
Once you get to this page, find your router (the ID should be on the bottom or the manual) and click on it. This will bring you to a game list. From here, head on down to the T's and find TDU. Follow the steps it tells you and if you do it right, thats one less thing that could be wrong with your game! (The ports are located on the final page I mention here, I couldnt be bothered to post them :p)
I'm very tired at the moment, so if anyone has suggestions I can add them to this post!