Here's a quick and dirty method of achieving the infrared effect.
1.) Open the Curves command via Image>Adjust>Curves or Cmd (Ctrl: PC) M.
2.) Right underneath and to the right of the adjustment area in the Curves dialog box are two buttons side by side. One of these looks like a curved line with points plotted on it and the other looks like a pencil. Click on the icon of the pencil.
3.) Make a series of short dashes in the adjustment area with the pencil tool. This inverts segments of the image while leaving the base colors unchanged. You can make the infrared effect as detailed as you want by adding more dashes in the adjustment area. See example below.
4.) For a variation on this effect, once you are done and have closed the Curves adjustment, Click Cmd (Ctrl: PC) I to Invert the image.
Hope this helps. Credit goes to Colin Smith @ photoshopcafe.com for this effect.
I've also posted my own example of this technique.