No matter what camera you have your photos will need some amount of Post proccessing in Photoshop, be ie leveling adjusting your levels and hue. But even if you have taken the perfect shot you will still need to crop the photo and resize it. This is where it gets a bit messy as a lot of pepole have different views on this but I find that 1024x683 to be the best for me. Some photographers use 1200x800. The level of proccessing is dependant on the camera you choose. The 300D is a good camera and a lot of photographers on a.net use this camera and have said nothing but good things about it. Where the real difference lies is in the lens you get. If your budget can stretch that far then get an L lens. An exelent value for money is the 70-200mm f4 L. This is very much an L glass lens but without the IS
. If you're looking for a lens that will cover a larger range then have a look at the 100-400mm LIS
. Still a very good lens. I'm not familiar with your area and therefore can't advise you on what focal length you need from where you want to shoot from.
I used to have the 70-300mm USM
III and have managed to get a few shots onto a.net but you need good light conditions, but that can be true for any lens you use really. If the light conditions are not good, i.e. dull and overcast day, you won't get good shots, maybe one or two but that's it.
Take care and good luck with your choice.