Your flexability with power point is limited and the bulk is inherant to PP files. I believe there are a few options for compression, but nothing that really makes them practical for the Internet over a dial-up connection. At least not w/o sacrificing the PP presentation and defeating the purpose of creating PP filles in the first place.
One alternative might be to Zip the entire presentation and offer it for downloading / viewing offline, depending on how important it is for your target audience to view the presentation. Of course, to do so the user must have PP installed on their computer to view the presentation, so I assume you have an audience that you're familier with and know they have the ability to view PP files.
Using Flash could give you an alternative to make your presentation display similar to PP and make the presentation more Internet friendly (file size and compatability). That's about all I can think of to tell you. Maybe someone else will have some other solutions as I've really only used Power Point to create workplace safety and anti shoplifting presentations to be displayed to employees using a projector....never really used it for Internet presentations.
"How did a fool and his money get together in the first place?"