Try these ideas.
A script that stays in the background, and at a certain time or interval, it shutdowns the current powerpoint, copies the the new files over and then restarts it.
I guess that depends on whether or not the remote computers have direct access to the powerpoint files. If not, maybe you could set up a small FTP server on the main computer, and write a script that downloads the files through FTP at a certain time on interval. Tell me what you think. That all can be done using Python that I know, and I'm sure you can write scripts in most other languages that will do the same.
If you need to see an example in Python let me know.
I realize this is for VB, but I'm just throwing out some more options.
Good luck
