There are two ways that the software on an iPod, iPhone or iPad can be updated. The first -- and simplest -- method is to just do a direct update. You can do this by clicking on the update button on the device's information page in iTunes, or just simply by letting iTunes continue with an upgrade when it automatically detects that new software is available. The second option is referred to as a restore.
Many users can easily be intimidated by this method, as at first glance, it infers that one might lose their settings or media if they restore their iPod, rather than updating it. The truth is that as long as you back up your device first, a restore isn't very much different from an update, other than the fact that it will take considerably longer to complete.
This is because rather than just attempting to update only the changed parts of the iOS software (as an update would do), iTunes completely erases the device, installing a 'clean' operating system, and then it restores your various settings and syncs your apps and music back to your iPod or iPhone. Once finished, your device will be in nearly the same state as it was prior to the restore.
If you are wanting to update to the new software, then why am I talking about restoring? Because apparently, the iPhone 3G needs to be restored, rather than updated, for things to work properly. We aren't sure why, but what we do know is that in order to get iOS 4 onto your iPhone 3G, you must do a restore (not an upgrade). While this may sound intimidating, rest assured that as long as you back up your device before doing the restore, things should go much more smoothly than they did when trying an update.
Did doing a restore help you get iOS installed on your device? Let us know in the comments below!