Right-click the first PNG file and click Edit
Ctrl+E to see width of single image.
Win+R
calc
[Enter]
(enter the width of the single image)
*, 5, [Enter]
(take note of result)
Alt+F4 to close calc
(type calc result as the new width)
[Enter]
Ctrl+PgDn (if it's XP / Vista) or Ctrl+PgUp a few times (if it's Win7) to zoom
Without closing the first image, open each of the other images and press Ctrl+A, Ctrl+C, switch back to the first and Ctrl+V.
Align the image and repeat for the next one.