I would suggest that you go to a camera shop and handle both of them. Some people don't like the feel of the 350D as it is pretty compact. They are both really nice cameras and you can't go far wrong with either.
Another thing to consider is that when you buy an SLR, you are actually investing in a lens sytem, rather than just buying a camera. As technology progresses, you will buy other bodies, but your lenses will last for a long while.
Have a look at the price and variety of lenses and see which system you prefer the look of. I use Canon, but that's a personal preference. Always buy the best lenses you can afford as cheap lenses can be a false economy.
Have you thought about the prosumer cameras that are around, instead of an SLR? Do you want to learn more about photography and try different creative effects or will you just leave it on auto and shoot away? The speed and flexibility of SLRs can't be beaten, but it's easier to take a bad shot with an SLR than a compact.
In respect to your question, it very much depends on the lens you use for the situation you are in. They vary in speed of autofocus and amount of light they require. A fast, long lens (fast = wide maximum aperture, long = long focal length) would be great for evening concerts but maybe overkill for bright daylight. A lot of the time you have to weigh up the pros and cons when you make a purchase decision.
Hope I've provided some more thinking points, feel free to ask any questions.