Do you want to find x where f(x)=g(x) for two functions f and g? If so, you can use the "Zeroes and Extrema of f(x).vi" VI under the Mathematics >> Calculus palette. This is in LabVIEW 6; not sure where exactly it is in earlier versions.
I attached a simple example. Also see the built-in examples for this sort of thing under Help >> Examples, then Fundamentals >> Analysis >> Mathematics Examples >> Polynomial Roots.
Hope it helps,
John Lum
National Instruments