A 5250 terminal emulator is already written for linux:
http://packages.debian.org/stable/net/tn5250

I downloaded the arm deb to my linux box and unpacked it:
ar -x tn5250_0.16.5-12_arm.deb
which resulted in two files. I unpacked data.tar.gz:
tar -zxvf data.tar.gz
which gave me all the install files. I then took the tn5250 file from the bin directory and the lib5250.so.0 file from the lib directory and placed the lib into /var/lib/install/usr/lib and the bin into ~/ on the 770.
After that I was able to see the help printout for the working 5250 client.

This may seem like a pain in the ***, but it goes to show how nice it is to have the power/repository of linux/opensource programs at your disposal. I would assume that someone will simply repackage the deb so it will do all this for you in the near future. (I would, but I don't know how to _yet_)