This is a guest article from laptopical.com, a great resource for apple laptop reviews and the latest news.

iChat is a useful program, and many people use it simply for messaging or video chatting. However, it is possible to get more functionality out of iChat than just video conferencing. You can use it to send a file directly to someone, or you can choose to share a live copy of the file with your friend using iChat Theater. This tutorial is for OSX Leopard.

First, open up iChat and log into your messaging program. Once you’ve done that, select the person you wish to talk to by either clicking the icon by their name in your buddy list or going to the File menu and selecting New Chat With Person. At this point you can begin video chatting as you normally would. The person you’re talking to won’t need a webcam for this or any other part of this guide to work – they will still be able to see you and the files you share as long as you have a webcam installed, iSight or otherwise. Just right click on their name in your buddy list and invite them to a “One-Way-Video-Chat” and you’re all set.

Next, locate the file you wish to send or share and simply drag it onto the Video Chat window. It can be a document, a picture, a movie – anything. A prompt with two boxes will come up asking you if you want to send the file or open it with iChat Theater. If you just want to send them a copy, this is where the guide ends for you – simply drag the file to the first box and it will transfer instantly. If you wish to share the file with them so that you can both look at the file at the same time, drag it to the second box. You can also select the File menu and click “Share a File With iChat Theater”.

Sharing a Keynote Presentation

Now that you’re sharing your file with the person you’re chatting with, a window will open alongside the Video Conference window with your file in it. This is the same exact image that the person on the other side can see. As the initiator, you have complete control over how the file looks. That means you can scroll down a document to a certain point, zoom in on a picture to emphasize a particular section, or breeze through a movie to the exact clip you want to show them. The other person can “look but not touch”, meaning they will see all your changes but can’t change anything themselves. This can be useful for illustrating exact points that might be tough to describe in words.

And that’s it! Sharing files with friends and colleagues has never been easier. When you close the window you can go back to video chatting as normal, or you can start the process all over again with another file.

[Matt adds: As far as I know, you don’t even need a webcam yourself. Just go to “Share a File with iChat Theater” in the File menu to start the process from outside a video chat. You’ll see that iPhoto has a separate option to allow you to access photos within your iPhoto library. Also, note that only files that work with Quick Look will work in iChat Theater.]