1) Add a timer object to your form (I believe it is under "Components" in the toolbox)
2) Set its interval to 1000 (it is in milliseconds
3) Add an event handler to its "Tick" event
4) In the event handler put something similar to:
mylabel.Visible = Not mylabel.Visible
5) Set the timer to enabled
That should do the job.
Or you could make a custom control "MyBlinkingLabel" add a label and a timer to that so that it is all encapsulated in one place.
Or you could do the timer control bits in code.
There are various options available to you.