Canon D30 has a
3.0MP APS-C (22.7 x 15.1 mm ) sized CMOS sensor . On the other hand, Nikon D3000 has a
10.0MP APS-C (23.6 x 15.8 mm ) sized CCD sensor and features Expeed processor.
Nikon D3000's sensor provides 7MP more than Canon D30's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the D30 and D3000 sensor size comparison.
Canon D30 and Nikon D3000 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.