function rollimage(sel,newimage)
{
 (newimage)? document.images['opc'+sel].src = bs[sel].src : document.images['opc'+sel].src = bs[sel].nrm;
}

bs = new Array();
bs[1] = new Image(); bs[1].src = 'images/bot_1_on.jpg'; bs[1].nrm = 'images/bot_1_off.jpg'; 
bs[2] = new Image(); bs[2].src = 'images/bot_2_on.jpg'; bs[2].nrm = 'images/bot_2_off.jpg'; 
bs[3] = new Image(); bs[3].src = 'images/bot_3_on.jpg'; bs[3].nrm = 'images/bot_3_off.jpg'; 
bs[4] = new Image(); bs[4].src = 'images/bot_4_on.jpg'; bs[4].nrm = 'images/bot_4_off.jpg'; 
bs[5] = new Image(); bs[5].src = 'images/bot_5_on.jpg'; bs[5].nrm = 'images/bot_5_off.jpg'; 
bs[6] = new Image(); bs[6].src = 'images/bot_6_on.jpg'; bs[6].nrm = 'images/bot_6_off.jpg'; 

with (document)
{
document.writeln('<a href="lab.html" onFocus="blur()" target="_self" onMouseOver="rollimage(1,1);" onMouseOut="rollimage(1,0);"><img name="opc1" src="images/bot_1_off.jpg" width="83" height="25" border="0" alt=""></a><a href="cad.html" onFocus="blur()" target="_self" onMouseOver="rollimage(2,1);" onMouseOut="rollimage(2,0);"><img name="opc2" src="images/bot_2_off.jpg" width="126" height="25" border="0" alt=""></a><a href="mat.html" onFocus="blur()" target="_self" onMouseOver="rollimage(3,1);" onMouseOut="rollimage(3,0);"><img name="opc3" src="images/bot_3_off.jpg" width="79" height="25" border="0" alt=""></a><a href="prot.html" onFocus="blur()" target="_self" onMouseOver="rollimage(4,1);" onMouseOut="rollimage(4,0);"><img name="opc4" src="images/bot_4_off.jpg" width="67" height="25" border="0" alt=""></a><a href="casos.html" onFocus="blur()" target="_self" onMouseOver="rollimage(5,1);" onMouseOut="rollimage(5,0);"><img name="opc5" src="images/bot_5_off.jpg" width="59" height="25" border="0" alt=""></a><a href="precios.html" onFocus="blur()" target="_self" onMouseOver="rollimage(6,1);" onMouseOut="rollimage(6,0);"><img name="opc6" src="images/bot_6_off.jpg" width="72" height="25" border="0" alt=""></a>');
}