Do you want to do this serverside or client side?
To do it client side you need to use javascript.
Code:
<html>
<head>
<title> </title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" href="style.css" type="text/css">
<script>
function GetAction(){
primaryinsurance = document.input.primaryinsurance.options[document.input.primaryinsurance.selectedIndex].value;
if(primaryinsurance == "bcbs" || primaryinsurance == "nobbs" || primaryinsurance == "nobbspos"){
document.input.action = "presert.asp";
document.input.submit;
}
else{
document.input.action = "nopresert.asp";
document.input.submit;
}
}
</script>
</head>
<body bgcolor="#FFFFFF" text="#000000" topmargin="0" leftmargin="0">
<form name="input" method="get" action="" onsubmit="GetAction()">
<select size="1" name="primaryinsurance" id="primaryinsurance">
<option value="#" selected>Select Insurance
Company</option>
<option value="bcbs">Blue Cross Blue Shield HMO</option>
<option value="nobbs">Blue Cross Blue Shield HMO New England</option>
<option value="nobbspos">Blue Cross Blue Shield POS</option>
<option>Blue Cross Blue Shield POS New England</option>
<option>Blue Cross Blue Shield PPO</option>
<option>Blue Cross Blue
Shield Direct Pay</option>
<option>Blue Cross Blue Shield For Seniors</option>
<option>Medicare</option>
<option>Medicaid</option>
<option>Tufts Health Plan</option>
<option>Tufts HMO</option>
<option>Tufts POS</option>
<option>Tufts EPO</option>
<option>Tufts PPO</option>
<option>Tufts Navigator</option>
<option>Tufts Liberty</option>
<option>Tufts Carelink</option>
<option>Tufts Medicare Complement (TMC)</option>
<option>Tufts Medicare Complement Plan (MCP)</option>
<option>Tufts Health Plan Medicare Preferred</option>
<option>Tufts Uniformed Services Family Health
Plan (USFHP)</option>
<option>Havard Pligram Health Care HMO</option>
<option>Havard Pligram Health Care POS</option>
<option>Havard Pligram Health Care PPO</option>
<option>Havard Pligram Health Care Best Buy
POS & PPO</option>
<option>Havard Pligram Health Care Best Buy
HSA (Health Saving Account)</option>
<option>Havard Pligram Health Care First Seniority
( A Medicare Plan)</option>
<option>Havard Pligram Health Care Nongroup</option>
</select>
<input type="submit" name="Submit">
</form>
</body>
</html>