Photo image quality - difference

Please, could anyone explain why photo images downloaded direct with Image Capture appear to be brighter, sharper and of better quality on the screen than those downloaded into iPhoto?

The difference is visible with both my cameras - a new Canon IXUS 85 IS and 4 year old Minolta DiMage 400. I have not been able to load any of the new Canon camera s/w - my internal DVD/CD burner/player is broken.
(I use a Power PC G4, 10.4.11, iPhoto 5.0.4, Image capture 3.0.3),

Thanks

Image Capture shows you the full, original image. iPhoto, since it's a catalog and has way more to do than IC, shows a proxy. You can control that, check prefs. Print them side by side, they'll look the same. Or open them in QT Player or Preview at the same time, they should look the same.

New Canon software can be downloaded form their site, also.

Photo image quality

Thanks BenB for your reply.
I do not print at home. Instead I send photo images from my iPhoto library on-line for printing to a specialist 'shop' elsewhere in UK. Does the slightly poorer iPhoto image quality on my Mac screen mean the printed photos will be lacking in quality, or will the original full quality image be printed for me?
A second question if I may. Would there be any advantage in downloading the Canon software or can I get by without it? I am not an expert user by any means!