Step 1: Get yourself a copy of Image Analyzer (it's freeware).
Step 2: You will need a visible image and a black and white (unenhanced) IR image from the same time. I've got two samples for you to use: Visible, Infrared
Step 3: Open the images in Image Analyzer in this order: Visible, Visible (again), Infrared.
Step 4: Convert each image to Grayscale by going to Image-->Grayscale.
Step 5: With the IR image on top, go to Image again, this time to Combine Images.
Step 6: Click OK, save, and you're done!
If all goes well, this is what your final product should look like:
