indeed depends each router has its system, there is a way to open ports but u have to know those things :
ur gateway and ur internal IP
my gateway is 10.0.0.138
my internal ip is 10.0.0.1
basicly what I do is go to "start"------>"run" and then I type "telnet 10.0.0.138" (but u should type ur gateway
then it asks u for username, I dont have any so I press enter but if u have a username u should know
then u do the next thing:
nat defserver addr "ur internal ip here"
nat save
system
reboot
exit the window and wait till ur router reboots, u should be done, I cannot guarrante it works man... but thats what works in my router!