Currently the part command and the addBookmarks...
command in prosper.cls is not very good. It completley
ignores the possiblity
of adding structure to the document like intended with
hyperref package. (Today it overrides much of hyperref
capabilities by using the Raw parameter in pdfmark.)
I suggest that somebody with insight in prosper (I have
tried but it is too complicated for me) integrates
prosper with hyperref or hypbmsec.sty (found at CTAN
etc) to make it easy to structure slide presentations
into sections, subsections etc.