Canon has an annoying and useless policy which makes it impossible to install the updates from their website without having an original cd. Apparently they want to make the lives of their customers harder than it already is. (My Mackbook Air doesn’t even have a DVD player!)
Lucky for us this website has some tricks to circumvent this. For me simply removing an update.plist file was enough to get ImageBrowser 6.7.2-updater (Mac OS 10.5-10.6) to installing without original cd.