Hello,
It sounds like what you want to do is better suited for a Waveform Graph or Chart than an XY Graph. You said you have a 2D array where each row has data you wish to plot vs. (I assume) its index in the array, which is what Waveform Graphs and Charts are for. An XY Graph is used when you have a set of data points that you wish to plot against another set of data points, and that doesn't sound like what you want to do here.
I have attached a sample VI (saved in LabVIEW 7.0 format) that shows plotting a 2D array of points to a Waveform Graph and to a stacked Waveform Chart, where each row is represented as a separate plot.
Hope this helps,
-D