Let's first explain a little about what forwarding and DMZ really mean/do... This will be in lamens terms so that you will understand it (not calling you stupid, so please dont take offense).
Port forwarding on a router, can be construed as two things because different routers use different terminology... One is the easy one. It is talking about your router firewall. This is to say that you are telling your router that you want to make sure your router relays the packets that your pc sends to where they need to go, or blocks them, according to how you have them set up. This CAN be used for simple home use, but is better used on the business end of things.. This way the IT can block or send ANYTHING they want from a router level and not have to set up EACH machine with firewall sofware...
The other defenition (and more standardized meaning), is this: You have an external IP address. This you know because you had to use a DynDNS type of site to NAME your ever-changing IP address (read dynamic IP address). Now, let's take a web server for an example of using this meaning of port forwarding. If you wanted to set up a web server on your pc, so that the outside world would see your web page you had set up on your machine, when they type in somethingorother.no-ip.info, you would have to tell your router that you pc IS in fact connected to that external IP address...
Your computer has an internal IP address. In fact all your computers BEHIND the router have a specific IP address that is only reachable from within your own (Local Area Network)... Well, we have to make sure that the REST of the world can also reach that internal IP address.. The way to do this is to use port forwarding.. This tells your router that the internal IP address 192.168.1.x (where x is whatever number you have listed as your IP address for the pc in question), should be the address that is accessed when someone tries to access somethingorother.no-ip.info...... So in your router settings, you would tell it to assign the internal IP address to be accessed when someone actually types in somethingorother.no-ip.info, and of course you can take it a step further and tell it what port that SHOULD be, or even a range of ports (port 80 being the standard web browser port)...
Now, DMZ stands for Demilitarized Zone, and just like you would think this means the same thing... When you put a computer on DMZ, you are actually putting it outside of the protection that the router offers you... It is essentially a way to tell the router "Hey, I dont want your protection, so put THIS machine outside, so the rest of the world sees this computer as NOT behind a router"... It is actually a little more complicated than that, but that will suffice where you are concerned...
In your case you MAY not have to worry about using DMZ, as some routers will let you forward ports without having to put THAT pc on DMZ. But, some routers will not allow this unless you DO put it on DMZ...
Go to the website that makes your router, as they should have a manual that should help you set this up (they are all different, this is why the board here assumes that you know how, because it is NOT a standarization in routers, Linksys is TOTALLY different than Blitzz, for eg..)... I hope this help explain a little better whats going on inside your router, so you can better fix it...
BTW, you acces your settings in your router by opening up your web browser and typing in the address that your router is set to.. This is different for each router so I cant help you there either, but check the documentation on the router as it should tell you the default address and the UN/PW that will access it...
[edit] Sheesh everyone was quick to answer this one.. I started typing this when there were NO replies, so take from this guide what you will... But hope it helps you better understand the basics of what is going on behind the scenes....
