In Jaunty [and presumably later releases, including any release you're likely using]1 the default file has been broken up into includes. The append line can be found in /ubuntu-installer/i386/boot-screens/text.cfg:
In Jaunty [and presumably later releases, including any release you're likely using]1 the default file has been broken up into includes. The append line can be found in /ubuntu-installer/i386/boot-screens/text.cfg: