To open PowerPoint slide show presentations without having the software on your machine all you need is the viewer.
Go to the Microsoft website and on to the Downloads area.
Type in a search for PowerPoint viewer 2007 in the page search box. Your search will return listings and you will see the PowerPoint Viewer 2007 as the first link. Click on this link and you will come to the download page.
Read the Oveview and System Requirements sections prior to proceeding to the download.
Select your connect type from the drop down menu. You will see Dial-up, Cable or T1.
Then click the download button.
Since you will be downloading the PowerPoint Viewer 2007 you will be able to open any PowerPoint file. Lower versions work fine with the higher viewer.
Since the 2007 viewer allows you to view presentations created in PowerPoint 97 and later. you will be well on your way to enjoying any presentations you receive.