You can use serial port and is very easy, the communication between pic and printer
the parallel port is more tedious and usb is very dificult.
http://www.posintl.com/support/documentation/hardware/1000prog.PDFread page 42 codes command and ascii
you can use protonplus or picbasic
define speed desired read manual proton plus samples in rsout communication
use resistor 1k between pin pic and pin rx printer and commun boot sides
use rsout <command> , < characters to print> , 10,13
rsout <command> , < characters to print> , 10,13
rsout <command> , < characters to print> , 10,13
rsout <command> , < characters to print> , 10,13
rsout <command> , < characters to print> , 10,13
and you need read the manual (RFM)

user to see commands.