I just wrote a paper on infrared photography for my History of Photography class a few weeks ago...although I have not done the method yet
there are filters that produce the effect. The filter blocks wavelengths that are NOT infrared, allowing infrared "light" through to the lens.
but you can also have a camera modified. The only problem with this is that you cannot reverse the procedure...you must be willing to have a dedicated camera for infrared photography.
You can reverse the process. The shop that did my conversion can put the original filter back in. I think they charge just as much as when the convert to IR.