Shared hard drive with user-level permissions I have a Drobo attached to an always-on Mac mini, with a bunch of files I want to be able to access from other computers. Some of them (DVD rips, photos) I want to be available to anyone on my network, and some (backups, personal file storage) I want to restrict to certain users.

I know that I can change the permissions for different folders by modifying the "Sharing &amp; Permissions" attributes in the "Get Info" window, but how does that work if the user is coming from a different computer? Obviously that's no good if someone can just make a new user on their own computer with the same name and then have access.

All machines are running OS X Lion. Is this something I need Lion Server for?
The "Sharing and Permissions" attributes are directly related to other users on your computer. In System Preferences, you can enable "File Sharing" which allows others on your network to connect to your machine and access folders that you designate.
In the configuration for File Sharing, you designate "Shared Folders". You can set them up to be read (or even written to) by "Everybody" or only designated users. Those designated users would need to have an account on your machine to authenticate themselves; the name of their account on their own machine isn't the factor here.

None of this requires Lion Server.