We used http://pixlr.com/editor to make the negatives for our project. In pixlr, choose "Open Image from computer" and select the photo you want to work on.
Once your image is open, choose "Adjustment" and then choose "Desaturate" to turn it into a black & white photo.
Next, choose "Adjustment" and then choose "Invert" to convert the image to a negative.
You are now ready to print your negative.
Before you print, make sure to set up your printer's settings to print in greyscale or black & white. You do not want any color ink to print onto your negative.
Print the negative & you are ready for the next step.