

This is unfortunately yet to be the case on OS X. On any other operating system, you can set up a private VNC session using almost any resolution you want, within a certain realm of feasibility.

Note that on all previous versions of OS X, logging in as an allowed user could only put you on the console session, possibly colliding with a console user if they were actively working on the system at the same time. That is commonly referred to as the "console" or "physical" session. If you're unsure of what I mean by "console", the console is the one and only session that a user directly attached to the computer via keyboard/mouse/monitor can use.

That new user will have a private session to work in, and the console user will go uninterrupted. This is accomplished by enabling VNC, and logging in as a user that is not logged in at the console. In Lion, OS X finally gained the possibility of having truly virtual sessions, meaning that they aren't displayed on the console.
