Don't worry, it's a bit cumbersome but doable if you take your time and follow the instructions.
First, you'll need to set a static local IP address for your computer so that it's local IP won't change. This is explained rather well on
http://portforward.com/networking/staticip.htm (no need to install their application).
Once you set a static IP, you'll need to connect to your router's administration interface and play a bit. Grab the user manual of your router from
http://download.comtrend.com/CT-5611.pdf (1.9 Mb pdf file). Then fire up your browser and go to
http://192.168.1.1/ and enter your login and your password (root and 12345 if you use the default values, I suggest you later change them for security reasons).
Then on the left side of the page, click on Advanced Setup, then on NAT and finally on Virtual Servers. (These settings are explained on page 50 of the user manual, the part beginning with "6.3.1 Virtual Servers", refer to it in case something isn't clear.)
There, click on Add, and then do the following:
Click the Custom Service radio button and enter ShareazaTCP in the box next to it as the service name. The Server IP Address you'll have to enter is the one given by the ipconfig command you used when you set a static local IP for your computer. It should look like 192.168.1.x, with x>1 (192.168.1.1 is the IP of your router, so the local IP of your computer needs to be different).
There, for External Port Start enter 6346
for External Port End enter 6346
for the Protocol choose TCP
for the Internal Port Start enter 6346
for the Internal Port End enter 6346
Click Save/Apply. You now have the port forwarding for TCP done.
Click on Virtual Servers on the left side again, and then on Add, and then do the following:
Click the Custom Service radio button and enter ShareazaUDP in the box next to it as the service name. The Server IP Address is the one you used for the previous entry.
There, for External Port Start enter 6346
for External Port End enter 6346
for the Protocol choose UDP
for the Internal Port Start enter 6346
for the Internal Port End enter 6346. Click Save/Apply. The port forwarding is now done.
At this point disconnect Shareaza from the P2P networks and then reconnect it (a radical way of doing this: quit Shareaza -I mean close it, not just minimize- and restart it). Finally, click on the Help menu and there on Connection Test to see if everything's OK.
Feel free to reply if something isn't clear (and tell which version of Windows you're using). If what I told above really sounds like Chinese, you can also tell your timezone in private so that we can find a moment to meet on IRC and get this sorted out.