function SelectAll(id)
{
	document.getElementById(id).focus();
	document.getElementById(id).select();
}


function clearText(thefield)
{
	if (thefield.defaultValue==thefield.value)
	thefield.value = ""
} 


$(document).ready(function()
{


	$('input[name="loginpopup"]').click(function() 
	{
		
		$('#popup[name="registreer"]').animate(
						{
							opacity: 0,
							marginTop: "700px"
							
						},"slow");
		
		$('#popup[name="loginpopup"]').animate(
						{
							opacity:1,
							marginTop: "400px"
							
						},"slow");
	});
	
	$('input[name="registreer"]').click(function() 
	{
		$('#popup[name="registreer"]').animate(
						{
							opacity:1,
							marginTop: "400px"


						},"slow");
		
		$('#popup[name="loginpopup"]').animate(
						{
							opacity:0,
							marginTop: "700px"
	
						},"slow");
	});


	$('a[name="closelogin"]').click(function()
	{
		$('#popup[name="loginpopup"]').animate(
						{
							opacity:0,
							marginTop: "700px"
	
						},"slow");
	});
	
	$('a[name="closeregistreer"]').click(function()
	{
		$('#popup[name="registreer"]').animate(
						{
							opacity:0,
							marginTop: "700px"
	
						},"slow");
	});
});

<div id="popup" name="loginpopup">
	<div class="close"><a href="#" name="closelogin"><img src="images/popup-close.png" alt="close" /></a></div>
	<h1>Administrator login</h1>
	<p>Beheer hier uw website</p>
	<div class="img"><img src="images/login.png" alt="login" /></div>
	<div class="form">
		<form method="post" action="?p=login">
			<input type="text" id="naam" name="naam" value="Sitenaam" onclick="SelectAll('naam');" />
			<input type="password" id="pass" name="pass" value="wachtwoord" onclick="SelectAll('pass');" />
			<p class="left"><a href="?p=wwvergeten">Wachtwoord vergeten?</a></p>
			<button class="button-popup" type="submit" name="submit">Login</button>
		</form>
	</div>
</div>
 
<div id="popup" name="registreer">
	<div class="close"><a href="#" name="closeregistreer"><img src="images/popup-close.png" alt="close" /></a></div>
	<h1>Registreren</h1>
	<p>Maak hier je spel aan</p>
	<div class="img"><img src="images/register.png" alt="image" /></div>
	<div class="form">
		<form method="post" action="?p=aanmelden">
			<input type="text" id="site" name="site" value="Sitenaam" onclick="SelectAll('site');" />
			<input type="text" id="user" name="user" value="Naam op de site" onclick="SelectAll('user');" />
			<input type="password" id="passw" name="pass" value="wachtwoord" onclick="SelectAll('passw');" />
			<input type="password" id="repeat" name="repeat" value="wachtwoord" onclick="SelectAll('repeat');" />
			<input type="text" id="email" name="mail" value="Email" onclick="SelectAll('email');" />
			<button class="button-popup" type="submit" name="aanmelden">Registreer</button>
		</form>
	</div>
</div>