476382 Find Hidden 4 letter codes in a string about 5150 characters

I have a string of approximately 5150. It might even be in a foreign language. I want a program that if I write into an input box a 4 lettered word and press enter, the program will search in equal intervals from 1 to 1715 where my 4 lettered word might be encoded into the text. so for example if I type in the name JACK and have a string xbJJrAAnCCpKKvv the output will tell me that JACK is encoded by the 3rd element of the array, the 6th element, the ninth and the 12th It is also encoded in the 4th,7th,10th,13th elements of the array. Clarification:Elements in the array which contain the 4 letter name in short intervals, need to be searched again to see if they are also contian the 4 letter name for longer intervals. The program must be written in a language usable by windows xp without having to install any special program on to the computer.