I am not sure but I think to way people make there own font is in PS and then code it or something, then for cod4 just convert it, but that is a wild guess, you want to start by learning to make a font first, google it buddy
Convert gamefonts.iwi to DDS open it in Photoshop, switch to the Alpha channel (uncheck the others ) . There you will see several characters, letters and numbers. You have to manually replace the simbols one by one. (Make sure you all of them has the same size or it will suck ). Convert it back to dds, and you can put it in your mod's iwd or to your "public skins" iwd .