If you are using this for the purpose of de-bugging your program, I like the idea Tomoya wrote about using a probe to see what is going to the text file. It's very simple.
If you are trying to do this at runtime, I would handle it this way : In a loop seperate from the one that does the writing, use a file properties vi to get file size and compare it to the last file size query (use a shift register for this). If the file size has changed, re-read and display the contents of the file to a front panel text box. Otherwise do nothing.
For a more programatically correct method, use a semaphore or queue to tell the update loop that its time to re-read. The writing loop would (after write) set the queue element (or semaphore). The reading loop would wait on this trigg
er to know when to read.
Jared