Need help with text input box

ok, i have a movie clip with lots of frame lables and i want a user to type in his or her postcode but when they click submit i want it to only pick up the first LETTERS only and then it will play the letter on the timeline and flash on the map where its corresponding place is, i have done the map animation i just need to know how to select the users first letters, bare in mind you can have postcodes like this…

OL10 4PF
M24 2DP
BL1 33A

for example on them i want it to take the “OL”, “M”, & “BL” and say gotoAndPlay(“OL”) OR (“M”) OR (“BL”) Cheers guys!! and gals!!!