re: "was just wondering how things work on the client end, once they receive a proposal with material attached... can the client download them straight onto their computer?"
Yes. They are downloadable files.
re: "It's just that I don't want to be giving away free material to strangers, should the proposal not go ahead!"
If you send a file to a client as part of a proposal, there is no way to prevent the client from doing anything she wants with the file.
