In that case, you can go to
Code:
Mathematics > Elementary & Special Functions > Trigonometric Functions
and select the atan2 VI.
Personally, I would just do this processing on the computer itself, not the NXT. It's not like transmitting each move will be much more data than transmitting the current location. However, I would (if it doesn't already) treat it like packets, and number each one make sure that data isn't lost. I suppose the location data could be sent back to the NXT in autonomous mode, to help with navigation.
For determining how far the 'bot has turned, the angle turned (in degrees or radians) is directly proportional the the "distance left drive has travelled" subtracted from the "distance right drive has travelled".