Yes, you can.
In earlier Microsoft Windows versions, all services and applications was running in the same session as the first user who logs on to the console (namely the Session 0).
Running services and apllications togeteher in Session 0 poses a security risk because services run at elevated privilege and therefore are targets for malicious agents. Since Windows Vista and higher OS (Windows Server 2008, Windows 7) services are isolated in Session 0, making this session noninteactive. The first user logs on to Session 1, the second to Session 2, making services protected from attacks.
In order to match this new communication management, we have modified consequently TightVNC, so that the remote control on a Vista computer (and higher OS) runs correctly.
Therefore, it is now possible taking the remote control of a Vista / 2008 Sever / Windows 7 computer(32 or 64-bit), even if any session is opened on the remote host (read more for a list of compatible OS).
In this case, the CTRL+ALT+DEL sequence should be send to the remote host (read more).
It is also possible to administrate and manage the remote host (regedit, services.msc ...) without being ejected from the remote host.
Finally, it is also possible to logoff the remote session, or also to switch user. Then the system will automatically detect this case, and a popup dialog like the one below will appear, giving time to the system to relaunch 'VNC Server' service on the remote host and to communicate through the different sessions described previously. After having hold on for a few seconds, the remote control should be operational.