The P100 takes acceptable photos.
Not excellent but not bad either.
You can improve your photo quality by not using digital zoom.

I don't know of any DSLR camera that has digital zoom.
Digital zoom is a crutch and it degrades the image.
One of the purposes of DSLR cameras is that if you want to get a closer shot you change lenses.

The Nikon D90 is an excellent choice.