Infrared Conversion Methods with Photoshop
Lets start out by opening the image you want to give the infrared(IR) look to in Photoshop.
I am using an image with lots of greens in it as it seems to work best for this IR conversion method.
Click the black and white New Adjustment Layer button on the bottom of the layers palette.
Once the New Adjustment Layer menu appears, select the Channel Mixer... option.
You should now have the Channel Mixer window opened. We now need to click the Monochrome check box located on the bottom left of the Channel Mixer window.
The set the following values:
Red: 100%
Green: 200%
Blue: -200% (this is NEGATIVE 200%)
Play around with the Constant setting until you get a look you like. I used -7% for my image.
That is it!
At this point I would save a copy somewhere on your system. Remember not to save over the original!
For comparison I added a couple other methods of IR conversion below.
Photoshop CS3 includes a new option to convert images to black and white. This option can be found under Images->Adjustments->Black and White... or by using the not so easy shortcut keys of Ctrl+Shift+Alt+B. The default settings gave me a look pretty close to what I got using the channel mixer.
Another option is using 3rd party plug-ins. Using Alienskin's Exposure plug-in I was able to simulate Kodak HIE IR Film. The plug-in is free to try for 30 days. It is a great set of filters.