Humans can see from about 400nm (violet) to 750nm (red). Below 400nm is ultraviolet light. Above 750nm is infrared. Infrared radiation has wavelengths between about 750 nm to about 1200 nm. Wavelengths used for photography usually range from about 700 nm to about 900 nm.
There are several solutions for taking IR pictures. For Film cameras you need infrared film which is both costly and hard to find. For Dslr's you need a camera capable of recording IR. The earlier Nikon cameras D1, D1x, D1h, and D2h are all capable of recording IR, with a IR filter attached to a lens. Cameras like D200 is not very good at IR photography as the low-pass filter blocks most of the IR radiation.
The cheapest solution to IR photography is to use a non-exposed but processed E-6 film strip as a filter.
Up one step is a IR filter. There are quite a few IR filters on the market, and which filter you should choose depends on the final result you want to achieve. The Filter I used before I converted my camera to IR was the B+W 77mm 093 F-PRO which removes the complete visible spectrum. Other filters don't remove the whole visible spectrum and gives some false color to the images. Another problem with a IR filter is that you can't see through the lens as a IR filter is opaque. You also need a tripod as the shutter speeds is far to low for handheld shooting.
The last and the way I currently take infrared pictures is to convert the camera to a IR camera. Dslr's have a low-pass filter, which stops infrared light to enter the sensor. By removing the low-pass filter and replacing it with a IR filter, the camera becomes as sensitive to infrared light as it was to normal light. The major benefit of this is that you can see through the viewfinder and easily compose your shots. There is also no need for long exposure times, and no need for a tripod. This is a huge advantage over the standard way of doing Infrared photography. The drawback with this is that you can only use the camera for infrared shooting.
Most of my lens reviews have Infrared performance rating, I will add the IR performance on the other lenses as well, as soon as there is time to do it.