Possible Duplicate:
Restore the Ctrl + Alt + Num Pad 4 and 6 window positioning commands?
Window Placement
Ctrl-Alt-Num 4 - Place window on the left side of the screen.
Ctrl-Alt-Num 6 - Place window on the right side of the screen.
How to make these two shortcuts work.
This wallpaper contains these two shortcuts.
You can try enabling the "Put" compiz plugin using the CompizConf settings manager. You might need to change the key bindings to match your preferences.