Sarah, Flash is the obvious choice today but i am an old Director guy with enough programming experience to be dangerous. Buttons or navigation will require learning code in either presentation, at least understanding it. Behaviors are provided, simple user friendly, drag and drop items.
Much depends on what you actually want to achieve. I can not state that enough. I use powerpoint all the time for shows and events, only speakers with big budgets, time and that are clear on the message in their speech get Director/Flash.
Been around long enough to know and avoid the visionary CEO with those tools.
While Director is cool (for me and other users) I’d shy away from it, I read somewhere Adobe does have plan to improve it but not sure why since Flash is so mainstream on the web.
Spicing up your powerpoint may be as simple as hiring someone to do your animations in flash and just supply you the file to import into ppt.
Brian