var ar = new Array("<IMG SRC=images/header1.jpg WIDTH=859 HEIGHT=168 BORDER=0>", 
"<IMG SRC=images/header2.jpg WIDTH=859 HEIGHT=168 BORDER=0>", 
"<IMG SRC=images/header3.jpg WIDTH=859 HEIGHT=168 BORDER=0>", 
"<IMG SRC=images/header4.jpg WIDTH=859 HEIGHT=168 BORDER=0>", 
"<IMG SRC=images/header5.jpg WIDTH=859 HEIGHT=168 BORDER=0>", 
"<IMG SRC=images/header6.jpg WIDTH=859 HEIGHT=168 BORDER=0>");

var num = Math.floor(Math.random() * ar.length);
document.write(ar[num]);