function doHeight(){
var x, y, msg='';

// for all except Explorer
if (self.innerHeight) {
x = self.innerWidth;
y = self.innerHeight;


// Explorer 6 Strict Mode
} else if (document.documentElement
&& document.documentElement.clientHeight) {
x = document.documentElement.clientWidth;
y = document.documentElement.clientHeight;


// other Explorers
} else if (document.body) {
x = document.body.clientWidth;
y = document.body.clientHeight;

}
z = ((y-600)/2) - 5
if(z<1)z=1;
return z;
}

/**
* valideer een e-mailadres
*/
function checkEmail(email){
  if(email != ''){
    var re = /^[a-z0-9\-\.\_]+@([a-z0-9\-]+\.)+[a-z]{2,4}$/i;
    if(!email.match(re)) {
      return false;
    } else {
      return true;
    }
  }
}