Both Olympus E-300 and Canon 350D have 8.0 MP resolution sensors but Olympus E-300's sensor is Four Thirds (17.3 x 13 mm ) and Canon 350D's sensor is APS-C (22.2 x 14.8 mm ).
Since Canon 350D'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 E-300.
Below you can see the E-300 and 350D sensor size comparison.
As seen above, Canon 350D has a 1.5x Larger sensor area than Olympus E-300. 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.