Question: How can I write to parallel port through Windows XP command line?

Answer: 
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.
Back in the DOS days we would frequently use a command like **type filename.txt > lpt1** to print our text files.