What is a SlideShare?

SlideShare is a free service for web sharing presentations and slideshows.
The service is run by SlideShare Inc, a startup based in Mountain View, California (USA) and New Delhi (India).
Slideshare supports several different types of presenting programs: PowerPoint, OpenOffice, Keynote, and PDF files.
SlideShare implements most common Web 2.0 design and interaction patterns. Like other social networking services, users are able to add tagging to their presentations. Rate and comment on others' work, and embed their presentation into a blog or other website. The site was created in late 2006 by an international pair--one in India, one in the US. The goal of the website is to help people share ideas.
There is no fee to use this service, though a login is required for uploading presentations. The maximum size for a slide show is 30MB. Shows that are larger, must either be edited or split into two (or more) presentations. Once a file is uploaded, it is visible to the public. Terms from slides can be searched via search engines. The user who uploads a presentation can choose to make the slide show available to be downloaded. Slideshare is linked with Creative Commons so various attribution licenses are supported. In addition, these presentations can be retrieved at any computer without need for USB drives or other storage devices. In other words, presentations in Slideshare can be held before a conference for the presenters use and then reviewed afterwards by guests. Like YouTube, a presentation can be viewed in the small screen or take the full screen of a monitor. (Source: Wikipedia)

Watch the embedded youtube videocast and more will be revealed:

What is Slide Casting?

Other excellent links:

Convert Powerpoint into a Video File: http://www.teachertube.com/view_video.php?viewkey=9c8cc8e70078a2597137
This tutorial shows you how to add Powerpoint and sound files to Moviemaker and this can then be saved as an AVI file.

another version of this - http://www.teachertube.com/view_video.php?viewkey=83519ec46d821b489b71

What is a Screencast?

A screencast is a video recording of the actions on a user's computer screen, typically with accompanying audio, distributed through RSS. Screencasts can be thought of as video podcasts. They provide a simple means to extend rich course content to anyone who might benefit from the material but cannot attend a presentation.
This tool is excellent for use as a tutorial site explaining what is on the screen in more detail.

Screencast.com has more information on this useful tool.