The computer’s parallel port can sometimes be rather fussy. For example, when I close the lid on my laptop and reopen it, the parallel port stops working. You might want to work out all of the quirks on yours before going to the trouble of designing a project around it.
Update: You might find the program on the page VB 2008 Program for Testing your Parallel Port useful for this task.
Warning: Before we go too far, I should mention that messing with parallel ports like this could fry your computer if it’s attached to the motherboard. Assuming that you don’t already have this type of parallel port to begin with, you can buy one that slips into the PCI slot in your computer. That way, only the parallel port will be damaged if something goes wrong. Hopefully 
Here is a picture of what I used to test the pins when writing the Sun Tracking / Heliostat Program. To really be certain that your parallel port is behaving appropriately, you can do something similar. Schematics for testing the parallel port can easily be found on the net. However, I have a somewhat less elaborate option available if you scroll down.
Take a 220 ohm resistor (red red brown) and wrap one end around the short wire of a led.
Next, The resistor end goes into pin 25 and the led end goes into pin 2 like you see in the picture below. If you look closely, you should hopefully see numbers that identify which pin is which on your parallel port.
With the led set up, start the sun tracker program and click the “manually realign” button. The below window should pop up.
Type “1000″ in the “Altitude” textbox for machine #1. Click the “GO” button while watching the led. Hopefully, you will see it light up for a few seconds and turn off. If it does, you have passed this stage of the test. NOTE: When doing this test, make sure to alternate between the number 1000 and 0 each time you run it. If you read the section of the tutorial on the “Manually Realign” button, you’ll see why.
Testing the Limit Switches
Another thing you can double check is if limit switches will work correctly with your parallel port. The first thing you need to do in order to run this test is make sure that the limit switches are activated under “Settings.”
Next, plug a wire into pin 25 and pin 10 like you see in the picture below. Note: I didn’t do it, but it wouldn’t be a bad idea to use the resistor here to make certain nothing is damaged if you plug it in wrong.
Making sure that Machine#1 is turned on, press start.
If all goes well, a window should pop up that says something similar to “Azimuth Limit Switch Triggered on Machine #1″
If you are unable to get the parallel port to work, you may need to change the port address. Go into device manager and find your printer port under “Ports.” Once there, go to resources and see if it is set to 378 like it is in the picture below. If it’s not, try the different settings under the “Current configuration” drop down list to see if any of them will change it.
If this doesn’t work, well then I’m not sure what you can do exactly. I’m still researching parallel ports myself, and I’m not clear on everything that can go wrong and how to fix it.
