function toggleLayer(whichLayer)
{
var option=['main','travel'];
if (document.getElementById)
{
// this is the way the standards work
for(var i=0; i<option.length; i++) 
{ style2=document.getElementById(option[i]).style;
if (whichLayer==option[i]){
style2.display = 'block'  }
else {style2.display = 'none'}}
} else if (document.all)
{
// this is the way old msie versions work
for(var i=0; i<option.length; i++) 
{var style2 = document.all[option[i]].style;
if (whichLayer==option[i]){
style2.display = 'block'  }
else {style2.display = 'none'}}
}
else if (document.layers)
{
// this is the way nn4 works
for(var i=0; i<option.length; i++) 
{var style2 = document.layers[option[i]].style;
if (whichLayer==option[i]){
style2.display = 'block'  }
else {style2.display = 'none'}}
}


}