For simplicity, let's say the user Administrator is logged in in terminal session 2. Another user Boda is logged in terminal session 3.
Is it possible to runas a program in session 3 from session 2?
For simplicity, let's say I want to start calc.exe in session 3 (in Boda's session). How do I do that? Can it be done with runas?

Like Harry Johnston suggested in a comment you can do this using the
psexectool available on TechNet. I've tried it using a Windows 2008 Server running Terminal Services and managed to start various applications in another users session (although not calc.exe - it started but minimized and the window refused to restore), among them cmd.exe.The command I used was
psexec.exe -i 3 cmd.exewhere3is the session number (that you can get fromqwinsta.exe).Example: Remote session, logged on as Administrator; using qwinsta to enumerate sessions and
psexecto startcmd.exeon another session.Another session: logged on as Patrick, with the
cmd.exewindow on the desktop opened by Administrator (which the window title reveals too).