the D90 is very new, so i couldn't tell you to be certain exactly how good it is, in my personal opinion putting video functions into a DSLR is simply a marketing sceme and may in tern wind up hindering the camera's overall preformance and reliability. This being said i wouldn't personally reccomend you go with it as a starter cam, the D80 and D200 have been tested and proven great cameras.
the CCD and CMOS sensors are the chips in the camera's that pick up the image, and are the reason everything works. the aperture, shutter settings and ISO settings control the basic use of the sensor and how much light needs to be on it to create the best possible image. Both CCD and CMOS sensors have there own advanteges, but in the overall current market of nikon/canon DSLR's CMOS has taken the crown in what is being used for the current cams.