Install Fake Sendmail (download sendmail.zip). Then configure C:\wamp\sendmail\sendmail.ini:
smtp_server=smtp.gmail.com
smtp_port=465
[email protected]
auth_password=your_password
The above will work against a Gmail account. And then configure php.ini:
sendmail_path = "C:\wamp\sendmail\sendmail.exe -t"
Now, restart Apache, and that is basically all you need to do.