If you select an image on one of your web pages in GoLive then look in the inspector you'll find a place to enter alt text. Whatever you enter here is the text that will pop-up.
You'll see this when using Internet Explorer, however that's not the standard way to do it, so browsers that follow the standards like Firefox won't show that pop-up text. If you want it to pop-up in all browsers you need to do as follows:
Select your pic from one of the web pages in GoLive and switch to source view. You'll see the image code high-lighted and look like this:
< img="dirpath/pic.jpg" width="60" height="60" alt="person name">
Notice the alt="person name". This is what you entered in the inspector and is what IE will show. For other browsers you need to add title="person name" so it looks like this:
< img="dirpath/pic.jpg" width="60" height="60" alt="person name" title="person name">