Go in to the System Bios (del,f1 or f2 usally) and make sure the LPT port(s) are defined as lpt1 io port 0x378 lpt2 io port 0x278 and not set to disabled or auto.
This is if the ports are build on to the system board, if it's an pci/isa board then the bios settings will not help. Might need to change jumper settings or load a dos based driver.
Dos under Xp is virtual, you will see issues trying to use a dos based program under xp when related to using serial/parallel ports. You need to run it under MSdos or Dr. Dos.