here is the code for password strength

in register.php
Code:
include 'functions.php';

..


<tr> <td align="right">Password:</td> <td> <input type="password" name="password" maxlength="30" style="width: 250" onkeyup="passwordStrength(this.value);"> </td> <td>*</td> </tr>

...

//displays the actual password strength realtime after each key is entered in password field
<table width="16%" align="left">
	<tr><label for="passwordStrength">Password strength</label>
		<div id="passwordDescription">Password not entered</div>
		<div id="passwordStrength" class="strength0"></div></tr>
</table>

..
in functions.php
Code:
<html>
<body>

<script type="text/javascript">
function passwordStrength(password)
{
	var desc = new Array();
	desc[0] = "Very Weak";
	desc[1] = "Weak";
	desc[2] = "Better";
	desc[3] = "Medium";
	desc[4] = "Strong";
	desc[5] = "Strongest";

	var score   = 0;

	//if password bigger than 6 give 1 point
	if (password.length > 6) score++;

	//if password has both lower and uppercase characters give 1 point	
	if ( ( password.match(/[a-z]/) ) && ( password.match(/[A-Z]/) ) ) score++;

	//if password has at least one number give 1 point
	if (password.match(/\d+/)) score++;

	//if password has at least one special caracther give 1 point
	if ( password.match(/.[!,@,#,$,%,^,&,*,?,_,~,-,(,)]/) )	score++;

	//if password bigger than 12 give another 1 point
	if (password.length > 12) score++;

	 document.getElementById("passwordDescription").innerHTML = desc[score];
	 document.getElementById("passwordStrength").className = "strength" + score;
}
</script>
</body>
</html>