I recently tried to build this program and ran into a few problems so I thought I would write this brief tutorial to help others avoid the problems that I ran into.
The following procedure has been verified with HPTalx 1.3.1a and Ubuntu 8.04 (both 32 and 64 bit).
1) Download and extract the latest version of HPTalx.
2) Extract the file, then open a terminal window and cd to the extracted directory (hptax-1.3.1a)
3) Get packages needed to build HPTalx
4) Get packages needed to run HPTalx once compiled
sudo apt-get install build-essential libglib2.0-dev libgtk2.0-dev libxml2-dev
5) Run configure script
sudo apt-get install libsocksd openbsd-inetd ckermit
6) Build HPTalx
7) Install HPTalx
8) Load hp4x module
9) Launch HPTalx
10) Click File-Setup and configure HPTalx for your connection interface
11) Put your calculator in server mode (see calculator manual or HPTalx manual/README)
12) Click Connect-Connect (or Ctrl-B) to connect to your calculator.