Hello! I've trying to find some existent libraries for ppt->swf conversion, but almost all tools I've found wasn't updated for a long time, or seems not suitable for this task. I has great experience with ActionScript, and I can do your project using C++ and ActionScript in such way:
1. Parse ppt file and produce ActionScript file, that would draw the same frames as in ppt file.
2. Compile AS files to swf using Flex SDK, which is free.
Please let me know if this approach is suitable for you. Possibly it will be useful for me to take a look on examples of ppt files you are going to convert.