Sampling radio frequency signals requires sampling rates in the GHz rate. There are no current NI data acquisiton products that can measure at those speeds. However, you can control a third-party specialized instrument through LabVIEW using GPIB or serial to accomplish this.
If you are only interested in intermittent impedance values of the circuit and do not require the higher sampling rates, then NI may have some daq modules that you can use. If you provide the specs of the circuit, then NI can help you select the hardware.
Once you have the data acquired, LabVIEW has Smith chart capabilities. There is the Smith Plot.vi located in the Picture Plots section of the Functions Palette you can use.Here's also a link of a Dev Zone example titled "Impedance Matching usi ng Smith Charts" that you might find helpful. http://zone.ni.com/devzone/devzoneweb.nsf/opendoc?openagent&DC09A87A6B634117862569DC005F5F9F&cat=FC2238B0E5929B7C8625696B007433DF