Go to File - Save As... and select PowerPoint Show (.ppsx). The presentation should open in slide show mode, but only if the receiver has PowerPoint 2007 or 2008.
If the receiving person has PowerPoint 2000-2004 (Mac or Windows), they will need to download and install the free Open XML converter from Microsoft in order to view your .ppsx file.
The other option is for you to save the presentation as a PowerPoint 97-2004 show.
Of course, you can also save as PDF which will reduce the chances that the person on the receiving end cannot open the file. However, you will need to get under the hood (so to speak) by setting it to open in full screen by using Adobe Acrobat (not just Adobe Reader, but the full Monty).
Ultimately, the best thing to do is to confirm ahead of time what version of PowerPoint the person on the other end is using, and then save it in a format appropriate for them.
Jeff
The best thing for you to do is to