Expanding on GerdW's answer, you will need to create a property node for each of the subsequent string controls by right-clicking the controls' nodes on the block diagram and selecting "Create»Property Node»Key Focus."
You can then right-click this and change it to write mode. You now have the ability to change the key focus to the appropriate field be feeding it a "true" boolean value.
In your event structure, you will need some kind of logic to determine which field the key focus is currently on (this can also be done using Key Focus property nodes, but in read mode this time) and then change the key focus to the next field accordingly.
Please let us know if you have any problems.
Eric V
National Instruments
Applications Engineer
Certified LabVIEW Associate Developer
"I'm a Ramblin' Wreck from Georgia Tech and a helluva (NI Applications) Engineer!"