If I may provide my two cents... if you have such requirements it would normally means you want a high level of security on your form. I would suggest using SSL so the connection between the browser and the server is encrypted. Both passwords and hashed passwords are visible on a non-encrypted encrypted connection, If you want to have a degree of security without SSL, there are libraries that will allow you to perform hashing from the browser
http://www.movable-type.co.uk/scripts/sha256.html" class="bb-url">
http://www.movable-type.co.uk/scripts/sha256.html. However, sending a hashed string is as bad as sending a plain password. If it gets intercepted, the hacker will simply send the same hash to impersonate you.
A better alternative is to receive a hash from the server on a random number (do not use the session number, it would be too obvious) and then hash the password, add the two hashes together to form a very long string, and hash it again. Then send this hash to the server, where you will repeat the process and compare.
It may sound complex but it isn't. However, the SSL solution is much simpler.