About the same with Ubuntu (GNome) and Kubuntu (KDE) then
I would have thought KDE would've turned on AA on the fonts by default. You can check for that under the KDE Control Panel > Appearance > Fonts > Tick "Use anti-aliasing for fonts". If it's already ticked, click on "Configure" and check that "Exclude Range" isn't ticked.
The fonts probably won't look as good as in Windows but it's better than the bog-standard ones (until you get TrueType fonts installed).