Edit your ~/.kde/share/config/kdeglobals file. There is a line for fixedQuote:
> > Hi everyone,
> > Can anyone give me a tip on how to change the fixed width font in
> > KDE 2.1.1 with anti-aliasing? The problem is something like this:
> > - I enable Anti-Aliasing
> > - As usual, all the fonts go wacky, and everything gets set to
> > the first TrueType font on my system (Agency FB).
> > - I change all of the fonts to Arial, Times New Roman, etc.,
> > however the fixed width font selection box has only _one_ font to
> > pick - "fixed." I pick "fixed" and click okay.
> > - I reload the font module, and the fixed width font has reset
> > itself back to Agency FB.
> > Is there anyway to force it to use a font such as Courier New, like
> > I can do in KDE 2.1?
font - set f.ex. Courier New there...