Windows xp2 (SR) has the facility, though I don't know how good it is. Type 'speech recognition' into the help and support.
Over several years I have been using Dragon Naturally Speaking,(up to version 9) now with 95% recognition, though it does take a great deal of training and patience. Ultimately its worth it - no more spelling mistakes, though to, too and two need sorting sometimes....
Certainly not free though!