First off, iMacs don't run iOS.
Secondly you posted in the Classic operating system forum which is only available for pre-2006 iMacs.
Third, we have no idea what web browser you are using or its version. So you have posted either in the wrong location, or given us insufficient details to find out why you may be having a problem.
Lastly, knowing whom your internet access provider is, and whether or not they have a proxy web server setting is critical to knowing if that might be a difficult.
Go to Apple menu -> About This Mac to find your Mac OS version. If it is X, you posted in the wrong forum. Here are the correct forums:
http://discussions.apple.com/docs/DOC-2463