Sounds like you want to build the same thing that already
exists as Adobe's breeze / connect.
What you're suggesting will require a lot of time/effort and
knowledge, and may require a reasonable budget depending on how you
do the media server side of things. If you have all those then
you'll be fine.
Converting from powerpoint to flash... I don't know.
The video and audio recording requires flash media server (or
red5 open source).