dock question on ibook

on my girlfriends ibook items keep dissapearing from the dock. they are still in the application folder but not on the dock. i ask if she is accidently dragging them off the dock and she says no. i believe her because its always the same ones that dissapear. it seems like anything that didn't come on the dock will be gone. if you put cocktail on there, word, powerpoint, macworks anything but what was on the dock when it started they eventualy all go away. seems like at the same time but i cant tell when they go away because im not using it. anyone have any ideas? i tried repairing disk permissions i cant think of anything else.

To keep it in the Dock, you have to actually drag the icon from the Applications folder to the Dock. When the app is open and running, the icon WILL show in the Dock, but as soon as the app is quit it will disappear unless you have saved it there previously by dragging and dropping it.

yea yea i know that. im saying you drag it to the dock it is on there with the app clossed for a day or so then it dissapears as if you draged it off onto the desktop. my bad i guess i wasn't clear on that.