I Googled D90 dead pixel and got quite a bit of information. It seems that if it is on your monitor, it is a relatively small issue in that it does not affect the output. A work-around if you will. Others say that a dead pixel on the sensor can be compensated for (repaired??) with Lightroom. One thing seemed evident was the question - are you sure? Or, why do you feel there is a dead pixel?
I'll be watching for responses and look closley at my D90.
Hope this helps.
"The Nikon did the work; I just happened to be behind it at the time." TP