Actually, on second thoughts, considering the 'DoF equivalency' varies, depending on which dimension of the sensors is compared, height, width or diagonal, I'll be generous and give you the 1/2 stop advantage of the 4/3rds system with respect to aperture for a given DoF. That leaves the 350D with only a 2/3rds stop advantage as a result of lower noise at high ISO's and less than that at lower ISOs.
I didn't realise the E-500 was so close. Well done Olympus! . However, pixel sharpness and detail in the E-500 images fall off at high ISOs, so it's really a bit difficult to put the E-500's performance on quite the same level as that of the 350D.
Perhaps a more significant disadvantage of the 4/3rds system is a lack of IS. The image stabilisation system in Canon lenses was the major reason for my switching from Minolta to Canon several years ago. Whilst IS is not of great use in all shots, for example those that require a fast shutter speed because the subject is moving, it is nevertheless a very desirable feature of ground-breaking proportions.
Olympus really needs to introduce an anti-shake sensor to remain competitive.