not done any infrared yet but as far as I'm aware there are several factors that cause problems
1) the camera has a filter over the sensor to cut out infrared light as it can interfere with some ccd's
2) it may be the frequency of light that the filter is cutting out, it may not drop enough visible light to produce a true infrared effect.
3) Did you take a custom white balance reading off a piece of white paer before shooting?
this webby should help though, pretty informative.....
http://www.wrotniak.net/photo/infrared/#POST