NAT vs msn messenger !?

i have a natwork sharing an ADSL internet connection using an Aztek turbo *00 router. the problem is that when usin msn messenger u cant send files or make voice confrencing, it boils down that u cant make a direct connectoin between a copmputer inside my network and the computer outside the netwok. i dont know how to solve this really , i heard of port forwarding or somthing similar , should i try it ? and could i do it ? and should open the same ports for all the computers in the network or should i specify a uniq prot for each computer ?

what do u think ?