LyX ⇒ output font is identical to screen font, why

[thobu]

this is for sure a newbie question. I'm having troubles setting a screen fotn w/out affecting the output.
My steps are: setting the screen font under Tools/, whereas I set the output fonts via Documents/Settings. Whenever I change the screen font to - say - sans serif I also get it in the output. That's not what I want.

Anything I'm missing here. Any help is appreciated. Thanks

[thobu]

is this really the only way to use - say - Georgia for Typewriter for the screen … under Tool/