Version: 2.4.5 (using 4.4.3 (KDE 4.4.3), Mandriva Linux release 2010.1 (Cooker) for i586) Compiler: gcc OS: Linux (i686) release 2.6.33.3-desktop-1mnb Most of the fonts used by Kalarm (menus, title bars etc.) are controlled by overall KDE configuration - except the central alarm text. If Knode had a "use custom fonts" option like Kmail and Knode then font control could be centralized. See also, <https://qa.mandriva.com/show_bug.cgi?id=58851>
You can set the default font for alarm texts in KAlarm's settings dialog. Each individual alarm's font can also be set in the alarm edit dialog.