How can I write to parallel port through Windows XP command line?
Looking at your reply to Zoredache, your real problem is not output to the parallel port, that's trivial.
Your real problem is how to get a 0xff character on stdout. This is possible with a trivial .com executable which invokes the relevant soft interrupt, but to be honest it's probably easier to create a file with that single 0xff character in it and then just copy that to the printer:
> copy /b data.bin lpt1
Note the /b flag which tells copy that the file is a binary file.