First, check the communication with the device with either MAX (Measurement &Automation Explorer) or Hyperterminal. This will verify the serial com parameters (baud rate, etc.) and that you're using the correct type of serial cable. Then look at the shipping examples for serial communication. The Basic Serial Write and Read and the Advanced SErial Write and Read differ mainly in how the terminalation character is sent at the end of each write. In the basic example, the termination character is included in the "string to write" control. The example uses a CR/LF (the \r\n). The advanced example shows how to use a VISA Property node to set a termination character. In this case, it's a LF). Your code should be pretty simple. You write the text using a VISA Write. Then, you could wait until VISA Bytes at Serial Port returns a non-zero amount and then keep reading until VISA Bytes at Serial Port returns a zero count.
There an awful lot of other examples (and questions) posted on serial communication. I answered one yesterday. A search of both this and the LabVIEW forum would help.
