PowerPoint 2010 includes a feature called Broadcast Slide Show. You can find in the ribbon after choosing the Slide Show tab. Click Broadcast Slide Show and then click Start Broadcast.
You'll need to enter a Windows Live ID, so if you don't already have one, visit Windows Live and sign up -- it's free. After that, your PowerPoint deck is temporarily uploaded to the cloud and you'll get a link to share with any number of remote viewers. Start the presentation, and they will see your slides in real time.
Note that this is not the same thing as sharing a copy of the deck for viewing at the recipient's leisure. The deck is only online and available for viewing only as long as you're broadcasting it, and they can't flip through the slides willy-nilly. They get exactly the same experience as if they were in the room watching the slides with you. Of course, there's no audio, so you will still need to include your remote attendees in a conference call. [via How-To Geek]
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