I just learned an important lesson - after 2 weeks of installing, uninstalling (repeated about 7 times) Adobe programs, the Adobe engineers said that Trial versions automatically default to US English. If a trial version is installed first, or the discs with US English, then the serial number will not work. In Australia, licenses are issued for International English only, hence the problem in that the issued serial number won't work.
I also found a good little application called 'Amnesia' http://www.apple.com/downloads/macos...osoftware.html available for both Universal and Mac, that removes every remaining item of a program AFTER you have uninstalled. Just find the remaining references in Applications (or programs) and drag them into Amnesia to remove all the rest of the stuff that was left over after uninstalling.
After uninstalling, reboot. For some people, it may be better to install in a separate folder like Applications2 (Mac) or Programs2 (PC) - but I was able to install into the default Applications folder ok. Enter the serial number immediately (ie don't do a trial first). And make sure International English is chosen in both places indicated.
Happily, everything is now resolved, although I have recommended that Adobe prints a paper note about this with all shipped software, and also put a notice with downloaded software because no-one knows this, as the Trials and the discs automatically default to US English.