Since Tiki 2.0 different icon sets are used:
The icons are indexed png8.
You need to transform the Famfamfam icons to png8. For this, for instance use the Gimp and
Some pictures from the admin section have been taken from Wikipedia Commons - trunk/pics/large/profiles.png, trunk/pics/large/semantic.png, trunk/pics/large/webservices.png
Icons can be overriden per theme if you place same file name in the styles/ThemeName/img/icons/
Also see Icon Fonts.