Play Videos halfsize by default?

[sidfrancis]

When I play HD-videos on my 24", VLC starts in window mode, but with a window nearly as big as fullscreen. When I resize that window, whether in play or in stop modus, after next start of VLC the window is big again, VLC doesn´t keep the windows size hat I set. After a reinstallation, everything works again, but after some starts, it forgets its size after being shutdown and starts very big again.
Is there any better way than always reinstall VLC?

[mederi]

Hotkey Z or Shift+Z
There is also some option in preferences to change initial Zoom permanently.