wants to connect Home server 2003 from outside via internet

1-I have configured the window 2003 server
2-I have Wireless router connect to NTL cable which have static ip but some time change.
3-i want to connect from office or friends home

when my friend connect via remotely to server
via static ip.but in home running lan private ip how router knows to my (server which have private address)
guide me plz.