Infrared test
Below are 100% detail shots showing the noise in infrared shots taken with the Nikon D200 at varying ISO settings. Here I used the green channel as being most indicative of the noise:
100ISO
200ISO
400ISO
800ISO
1600ISO
3200ISO
As you can see, noise is very well controlled through 800ISO. In all cases I had noise correction turned on, which significantly extending the shooting time at the lower ISO settings as a dark exposure is made following the actual exposure.
Below are some more images taken with the D200:
Red
Green
Blue
As you can see, the D200 is capable of some lovely IR photography, though it is not suitable for portrait and wedding IR work without either modification or with a very fast lens and high ISO setting.