My nikon d90 does not have blur in the backround? - 1

My old nikon d40x had that feat but my nikon d90 does not have blurry backround?

That's not a feature of the camera. It's an effect that's created by the lens when there's shallow depth of field in a photo. If you're using the same lens(es) you used with your D40x, you should (theoretically) have no problem creating the effect in the photos you're taking with your D90.

To deliberately get the effect, you need to create a shallow depth of field. Larger apertures produce nicer bokeh (that's the term used to describe the "pleasing blur" of out-of-focus areas of a photo) than smaller ones. Extend your lens to its longest focal length and get as close to the subject as possible. The further away from the subject the background is, the better the blurring of the background will be.