In the Chrome 11 browser, Google added support for HTML speech input API.
"With this API, developers can give web apps the ability to transcribe your voice to text. When a web page uses this feature, you simply click on an icon and then speak into your computer's microphone. The recorded audio is sent to speech servers for transcription, after which the text is typed out for you."
Google Translate becomes the first Google service that started using this feature.
If you are using Google Chrome 11 Beta, Chrome 12 Dev/Canary or a recent Chromium build -- just visit Google Translate, you can now click on the voice input icon. Right now, this feature only works for English, so you need to select "English" from the list of input languages.