Both Nikon D80 and Olympus FE-45 have 10.0 MP resolution sensors but Nikon D80's sensor is APS-C (23.6 x 15.8 mm ) and Olympus FE-45's sensor is 1/2.3-inch (6.08 x 4.56 mm ).
Since Nikon D80's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Olympus FE-45.
Below you can see the D80 and FE-45 sensor size comparison.
As seen above, Nikon D80 has a 13.5x Larger sensor area than Olympus FE-45. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.