Well, even if Killzone has solved the problem Yankme's entry needs clarification. It's not that complicated.
The headlines for intros, missions and outros are set in the description.ext. Open the description in notepad or similar program. Add these two lines at the top of the document:
onloadintro="your text here"
onloadmission="your text here"
What's written between the quotes in onloadintro will be shown BEFORE the intro loads, but also BEFORE any otro (win or lose).
What's written between the quotes in onloadmission will be shown AFTER any intro, but BEFORE the briefing screen pops up.
The excell document Yank is refering too is simply a string table. Inside his mission there still has to be a description.ext file that says
onloadintro="STRM_missionText"
onloadmission="STRM_missionText"
Otherwise his example will not work.
EDIT: By leaving the space between the quotes blank, you will not have anything but time and date, no "Get Ready", no nothing. The time and date will always be shown, though. Afaik there's no way to remove them.