Manuel, this is not a bad shot. First, let me ask you, is the ceiling textured? I am suspecting it is texture and not noise since the walls are nice and clean. Secondly, you have to remember that your camera is working very hard to get some kind of balance between the interior of the room and the bright window. In situations like this, I always do 3-5 exposures for HDR simply because there is no way that your camera can compensate for the bright light window and the dark interior.
I downloaded your pic into lightroom and CS5 on my computer and ran it through Dfine 2.0, and there was very little noise (almost none) in the pic. Look at your ceiling . . . is it textured?
If you're seeing "noise", you may want to find a lens with a max f-stop of 2.8 --that does help. By the looks of this pic,though, I don't think there's anything wrong with your camera. Remember that these cameras are really hi-res -- I am always amazed at how many wrinkiles I have when I do a self-portrait.
I gladly defer to my esteemed colleagues with more experience, especially with the d90. . . try photographing the interior WITHOUT the bright window and see if it makes a difference.
Best Regards