Sounds like Intermec Print Language. We use some Intermec printers at work, but mostly with stored labels and mostly via Delphi/Windows and nearly always over the serial port (using an in-house rs232 module). We have one system that uses Perl on HP-UX with the serial port. It writes the label data to a file and then does a system call to read the file with the 'cat' command and pipe the output of that cat command to the 'cu' utility, which does all the talking to the printer.

For a windows environment, I suppose you could do something similar by building your label up and then telling the shell to write it to the serial port.