I'm trying to do a false colour effect on my IR foto's, however I can figure out how to do a false colour by swapping Red and Blue channels.
What do I have to do to get a false colour effect in lightroom (4.1)?
Lightroom doesn't allow you to swap the colour channels in an image, you need to use Photoshop (or GIMP, etc.).
The easiest way to do this is to setup your channel-swapping program as an external editor (via Edit > Preferences > External Editing) in Lightroom (although if you use Photoshop it gets done for you automatically). Once this is done you can open the images in the editor from within Lightroom by selecting the editor from the context menu.