Slideshare is a site where you can upload your powerpoint presentations, pdfs, odp (OpenOffice) and they will save as a slideshow that you can click through. Keynote presentations need to be saved a pdf first.
Register first, and click on the upload tab to upload your presentation - 50MB limit.
Once they are uploaded you will be able to view your Slideshare as you would on Youtube. Look for the embed code, copy it and embed it in your blog as described in the Video post.
Note that your transitions, links and sound files will be lost in the upload. However, once your presentation has been uploaded you can add a podcast mp3 track to it and create a slidecast.
To get rid of those annoying and sometimes inappropriate trailers and advertising at the end of the slideshow just locate the parts of the code shown below and alter by typing in the bits in red.