Oriana,
it is simple: just create a while loop. It will run in parallel to the rest of your vi. Inside the loop, perform the task that you want to be done regularly. Also, add a delay function from the time/dialog palette. In LabView 7.1 (which I don't have), there is also a special timed while loop which performs its timing on its own. You need to wire something to the stop terminal in the lower right corner of the loop, like a local variable, that can be set from outside the loop to stop it when needed.
Regards
Matthias