I am recommending RoboHelp as the help authoring software for a suite of applications that I am documenting. Currently they are documented (kind of) in a mishmash of Help Scribble and PowerPoint presentations.
Is HelpScribble able to create a .CHM file? If so, you could reverse engineer the CHM and make it a RoboHelp HTML project. My colleague Peter Grainge has some good information on his site about doing this.
For the PowerPoint, you might consider opening in PowerPoint and saving as HTML. You could then import the HTML into the project.
Helpful and Handy Links
I never thought of capturing the PP file as HTML...
As for the HelpScribble stuff, I do have the source files, so I'm thinking there must be an easier way to convert to RoboHelp. Maybe not though. At least decompiling the CHM is one possibility (with help from Peter).