I'm sorry to hear that trying to upgrade gettext crashes your computer, but it's not possible for that to be gettext's or MacPorts' fault. There must be something wrong with your computer. Do normal troubleshooting: use Disk Utility to check if your disk is ok; take out one or the other of your RAM chips to see if one of them may be faulty, etc.
I also have a PowerBook G4 1.67 GHz running Leopard and it was able to upgrade to gettext 0.18.3.2 just fine. This model did however have some hardware problems, such as a defect in the lower RAM slot. That article only describes that the RAM would not be recognized in the lower RAM slot, however on my PowerBook, having RAM installed in the lower RAM slot causes it to crash within seconds. Removing the RAM from the lower slot and using only the upper slot has made the computer usable again; now it only crashes if I let it get too hot, so I try to elevate it off the desk a quarter inch or so to give it more airflow.
The latest version of gettext is 0.18.3.2 which was released January 7, 2014. See http://ftp.gnu.org/pub/gnu/gettext/?C=M;O=D . If it concerns you that the developers of gettext have forgotten to update their web page to indicate this, you should report that to the developers of gettext.
