The following shortcut keys are available from a Terminal Services Client:

CTRL+ALT+END opens the Windows Security dialog box.
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 in the order they were started.
ALT+HOME displays the Start menu.
CTRL+ALT+BREAK switches the client between a window (if applicable) and a
full screen.
ALT+DELETE displays the window's pop-up menu.

CTRL+ALT+Minus (-) symbol on the numeric keypad places a snapshot of the
active window, within the client, on the Terminal server clipboard (provides
the same functionality as pressing ALT+PrintScrn on a local computer.)
CTRL+ALT+Plus (+) symbol on the numeric keypad places a snapshot of the
entire client window area on the Terminal server clipboard (provides the
same functionality as pressing PrintScrn on a local computer.)

Notes

On an NEC98 computer, these are different in two cases:

CTRL+ALT+BREAK is replaced by F12.
The CTRL+ALT+END is replaced by F15.