As mentioned above, dust on the sensor is a fact of life with DSLRs. Keep a rocket blower handy to blow the dust off lenses and the sensor (when necessary), and minimize it by keeping dust in mind when considering when, where, and how often you change your lenses. Zoom lenses may reduce the frequency of lens changes, but the zoom action may also admit some dust. Take advantage of the D7000's sensor cleaning function to shake dust off the sensor (p 284 in manual). A little dust on the sensor is easily managed in post processing.
You can manage dust, but you can't stop it. With care in how I change lenses, frequent use of a blower to remove dust from the lenses and camera surfaces before and during lens changes, and employing the sensor cleaning function, I rarely notice dust specs on my images.