If you're going to do a lot of this, then you might want to invest in a piece of software called "FS Panel Studio" See: http://www.fspanelstudio.com/ You will only (really) be able to edit 2D panels, but that is usually all you're looking for.
I also recommend you do a bit of research. An internet search string like "making new pop-up panels in MS FSX" (or some such) might yield a mess of information in this day and age.
I'm writing this with no worries that I'm stepping on someone's literary toes. All of the copied and pasted stuff you'll see, below, is either my own text or copies of