Sattu, In windows platforms you can use Microsoft's Speech Software Development Kit (SDK). This is basically a library to convert text to speech and speech recognition. Creating your ouw speech recognition ruotines in LabVIEW is possible, however you will need advanced DSP knowledge, and a lot of time.
You can find more info on the Speech SDK at http://www.microsoft.com/speech/download/sdk51/ I hope this helps. Regards, Juan Carlos N.I.