Under normal conditions a time signal will be Real while the spectrum is Complex. It is easy to display the real time signal on a graph but, as mentioned earlier, to display the complex spectrum you normally convert the result into two real plots, respectively the magnitude spectrum and the phase spectrum.
There are ways of displaying complex arrays on a graph, for example using an XY-graph and displaying the real part on the x-axis and the imaginary part on the y-axis, but I don't think it is what you want to achieve. To read more about the topic (FFT, complex representation etc.), see for example the LabVIEW Measurement Manual (Chapter 13) "Frequency Analysis". You can access the manual when you launch the "Search the LabVIEW Bookshelf" either from your Start>>Programs>>National Instruments>>LabVIEW ... or from the Help menu of any VI window.
