Here is a list of the shortcut keys available on Screen Sharing connections:
ALT+PAGE UP: Switches between programs from left to right.
ALT+PAGE DOWN: Switches between programs from right to left.
ALT+INSERT: Cycles through the programs using the order in which they were started.
ALT+HOME: Displays the Start menu.
CTRL+ALT+BREAK: Switches the client between full-screen mode and window mode.
CTRL+ALT+END: Brings up the Windows Security dialog box.
ALT+DELETE: Displays the Windows menu.
CTRL+ALT+MINUS SIGN (-): Places a snapshot of the active window, within the client, on the server clipboard (provides the same functionality as pressing ALT+PRINT SCREEN on the local computer).
CTRL+ALT+PLUS SIGN (+): Places a snapshot of the entire client windows area on the server clipboard (provides the same functionality as pressing PRINT SCREEN on the local computer).