Yes MS word does have a built in one, but if you don't have Word, it's about $350 (so you might as well go with the other one.)
If you want to be serious about voice recognition, you can go as far as to download windows vista. It comes with a built in voice recognition system which works with Wordpad/Notepad/other text editors.
It may not really be worth installing another OS, but it's the only free way I know of. I typed about half of this message with it, and it worked pretty well.