I don't think you quite understand.
You can't just type in text into the FPIs and have it show that text. All of the text that shows up as default are all
images, not text.
You have to make your own .tga's using something that makes them, like Photoshop (if you've got deep pockets) or The Gimp (I think...). If not, you can just make it a transparent image (if possible, otherwise you'll have a white background around the text), in something like a .png, and then convert it to .dds or .tga (it doesn't
really matter) for use in FPSC.
You'll have to read Benjamin's thread on conversation scripts (use the search at the bottom of the page), which will basically explain all of your other questions for you--I'd assume that, anyway.
Evil has a new name. Demo out now!