Converting your presentation to .pdf can offer significantly enhanced security. You can protect your .pdf behind a password. Without the password, a browser will not easily be able to print your document or even to select and copy snippits of text for pasting into another document. The image resolution is excellent, and everything you see on your slides should come through accurately, though animations will be flattened.
For what it's worth, I tried selecting the option to include animations in the conversion, but I found that this made no difference. You can view both options below for yourself. To see the security in action, try copying or printing some of the text.
Browsers will not need PowerPoint, but they will need Adobe Reader. Many browsers presumably already have Reader, and it's a free download for anyone who doesn't have it already. Still, having to go through the download may discourage some individuals.
Depending on browser configuration, the .pdf may open and play within the browser. This can be convenient, but while it is loading (which can take a while) the browser will see a blank screen and think, perhaps, that the link is broken.
Perhaps more to the point, you will need to have Adobe Acrobat (or some other .pdf conversion software). Acrobat is large and expensive, but you can have your desktop support person help you get access to it. The integration between Acrobat and PowerPoint is smoother on the PC than on the Mac.
My .pdf files are slightly larger even than the original .ppt. They will eat up space in your account and they will be slow to download for browsers with slow connections. Even still, this approach is definitely a front-runner.
In a similar vein, you might consider converting your presentation into a QuickTime (.mov) movie.