Capturing Screenshots in Ubuntu

[Alfred Vahau]

Hi,
What is the Ubuntu way of capturing screenshots?
I need to capture screenshots for insertion in Impress presentation of 
OpenOffice.

PrintScreen followed by Insert has no effect. Nor is there a paste 
option on right click of the mouse
button after hitting PrintScreen key.

The old fashion way of Alt+PrintScreen followed by Alt+Shift+Insert too 
has not effect.

Pointers on how to capture the screenshots is appreciated.

Alfred,