Hi,
I found this diagram on a website somewhere. It shows you what can and can't be done, depending on user and creator versions. I have had this so long that I have no idea where it originated, so apologies to the person I borrowed it from!.
This was for ES2 - you basically have to have the Reader Extensions software for everything in Option 4 (including letting the user attach files). This is a server side application, which doesn't come as standard with ES2. It had to be purchased separately and was quite expensive.
For ES4, there are details about the Reader Extensions on this page:
Modules | Adobe LiveCycle Enterprise Suite 4
No idea of the cost of this one though.
Good Luck