Your mistakes
1) didn't delimit string literals (the single quotes I added)
2) Calculate random int at wrong time (also, use .floor(), not .round())
3) Broken concatenation attempt in document.write() that was also unecessary
Code:
<SCRIPT LANGUAGE="JavaScript1.2">
var arr = new Array(2)
arr[0] = '<a href="http://www.aratronix.com"><img src="aratronix.jpg" border="1" bordercolor="000000"></a><b>Aratronix</b> is a computer company whose layout was completed in June of 2003.';
arr[1] = 'More completed projects to come!';
var a = Math.floor(Math.random() * arr.length)
document.write(arr[a]);
</SCRIPT>