Unable to Log In after New Local Install

I have tried installing WordPress locally (on Vista) using both Xampp and Wamp, Once I have set up a database and local site and gone through the installation process (which seems to happen correctly) I am unable to login, I keep getting the wrong username/password error message.

I have been through absolutely everything I can think of, including going into the database through phpmyadmin and altering username and password etc.

I really have run out of ideas and I know I may be being thick or may have just missed something, but can somebody please, please help??

Thanks