Update #2: A SOLUTION!!
After a lot of seeking I finally found an 800 number to Canon USA support which helped a lot. The reason there is no Canon driver for the 300d is that it is included in Vista, a fact no one else bothered to mention. With some work with the very helpful support folks we were able to determine that the reason Vista did not work is that a change needed to be made to the camera itself. Just went to menu, then to the last 'tools' screen. about the 3rd choice down was changed ( I do not remember what the change was, but there are only two choices, try them til it works. When I then tried to download from the camera to the computer it worked fine. Hopes this helps.
Could I say the advice you gave was terrific. I have spent four hours trying to download my driver for my Canon 300D and was about to throw the computer out the window. Your helpful advice did it in 25 seconds. Great . All power to the Website. John