There's a couple of things you could do, both rely on you having PowerPoint (and preferably a later version like 2003 or 2000).
You will also need a web site you can put the file on so others can access it.
Essentially you need to save the presentation as a single file web page. To do this, go to File:Save as. From the save as window, select "Single File Web Page" rather than the default which is PowerPoint Presentation. This converts the slides into a series of images and HTML code contained within a single file. Put that file on your website and then post a link to that file.
This enables anyone to view the slides regardless of whether you have PowerPoint or not.
You could also select Save as Web Page from the file menu, this creates a series of HTML files and a index file, again, posting these to your website will allow others to view without requiring PowerPoint to be installed.
The final option you have is to create an Adobe Acrobat file of the presentation and again post that file to a web site.
I guess it's not that straight forward but at least its possible.
Give me a shout if any of the above is not clear.
Dave
