http://roberthogan.net/stuff/tn5250/

Step One
--------
Patch svn wireshark with tn5250-XXXXX.diff. You can do this by:

svn co http://anonsvn.wireshark.org/wireshark/trunk/ wireshark
cd wireshark
patch -p0 < /location/of/tn5250-XXXXX.diff

Step Two
--------
Compile wireshark:

./autogen.sh
./configure
make

Step Three
----------
Run wireshark:
./wireshark

Step Four
---------
You can then dissect the sample dump at:
 http://roberthogan.net/stuff/tn5250-dissector/tn5250sample.pcap.

To dissect a 5250 stream you select 'decode as' and then telnet. The telnet 
dissector will call my 5250 dissector when it recognises a 5250 stream.

It is quite possible that the 5250 streams you're interested in are not 
detected properly by the dissector. If not, please send on a sanitized dump 
to me so that I can try debugging it.

Email: robert@roberthogan.net