function  secBoard(n)
{
var pImg0 = document.all.bigimg0;

if(n==0)
{
pImg0.src ='images/main_a.jpg';
}
if(n==1)
{
pImg0.src ='images/main_b.jpg';
}
if(n==2)
{
pImg0.src ='images/main_c.jpg';
}
if(n==3)
{
pImg0.src ='images/main_d.jpg';
}

for(i=0;i<mainTable.tBodies.length;i++)
mainTable.tBodies[i].style.display="none";
mainTable.tBodies[n].style.display="block";
}