Folder permissions in Win 2003

I have a Windows 2003 server. I am trying to allow the group (Students) to be able to save files in a shared folder without giving them the ability to either delete or move the other files.
The problem I am having is that a student can (and does) go into that folder and deleted others or his own work.
I would like them to be able to save a file but to not be able to delete or move it.
So far I have had no luck with the normal folder permissions or the advanced ones. If I can write then I can also delete/move. If I can not delete or move than I can not write a file.