Siemens,
The easiest way is to use smit:
firstly type: ifconfig -a
This will list all available n/w cards and the respective addresses - i.e. which card the address you want to change is configured to if it is ethernet it is normally en0 i.e.
en0: flags=e080863<UP,BROADCAST,NOTRAILERS,RUNNING,SIMPLEX,MULTICAST,GROUPRT,64BIT>
inet 20.9.167.45 netmask 0xfffffc00 broadcast 20.9.167.255
Then type: smitty tcpip
Select minimum config. and startup
Select the n.w card as found above i.e. en0
In this screen change the internet address to what you want - press return et voila.....
Hope that helps
PSD
HAMCP specialist