Thank you all for you kind advices.
However, I'll try with KDE 3.5.10 to see if it works more consistent.
This is what I have now on openSUSE 10.3 and KDE 3.5
It shows Firefox, OpenOffice and KDE application. Note how the fonts are consistent, both in size and general appearance.
I admit that I had spent some time adjusting the font settings on 10.3 as well, but what drives me crazy is the need to do that with every new version of opensuse.
Cheers