Port forwarding help


Fully Optimized
Im going slowly insane here IM trying to port forward my 3com router for the last 2hours and am going round in circles can someone please tell me what Im doing wrong? Im not setting up a statc IP correctly ive been on the port forward website and it says

Enter your computers default gateway (so im putting in my router address)
Enter your computers current IP address( so that is my external IP address I think)
You then select find IP address and it gives me a list of static IP adress(5)
so I go into network connections and right click my network , select propperties and internet protocol tcp/ip propperties to get the box up, I click use following IP address now heres where im doing something wrong. the website tells me to put my static IP, in IP address box which I do but what goes in SUBNET MASK & DEFAULT GATEWAY

No matter what combinations ive tried onced ive saved the data I can not access the INTERNET. please can someone put me out of my misery and show me my errors of my ways.:confused: