Pass contents of field to URL

from the below code how do I pass the contents of the ‘username’ field to the end of the URL:

https://carrierconnect.etdatacenter.com/Default.aspx?accesstype=autologin&cust=id_015&user=username

where I currently have username

Basically the form works where I fill in the username and password then based on whether the user selects ‘customer tracking’ or ‘web booking’ goes to the specific URL

<script type=“text/javascript”>

function OnSubmitForm()

{

if(document.myform.operation[0].checked == true)

{

document.myform.action ="https://webtrace.etdatacenter.com/webtrace.aspx?accesstype=autologin&cust=id_015&user=templateuser";  

}

else

if(document.myform.operation[1].checked == true)

{

document.myform.action ="https://carrierconnect.etdatacenter.com/Default.aspx?accesstype=autologin&cust=id_015&user=username";  

}

return true;

}

</script>

<form name=“myform” target=“_blank” method=“post” action=“” onsubmit=“return OnSubmitForm();”>
<fieldset>
<legend><font color=“#FFFFFF”>LOGIN</font></legend>
username: <input type=“text” name=“username”/><br /><br />
password: <input type=“password” name=“password”/><br />
<input type=“radio” name=“operation” value=“1” checked=“checked”/><font size=“-1”>Customer Tracking</font>
<input type=“radio” name=“operation” value=“2” /><font size=“-1”>Web Booking </font>
<input type=“submit” name=“submit” value=“submit” />
</fieldset>

</form>

could someone take a look at this? The page is at www.meadowlarkco.com/indexnewsite_test7.htm

basically based off of which radio button is selected whether ‘Customerr Tracking’ or ‘Web Booking’ the user is directed to the appropriate URL and I need to attach the value of what is put in the username field to the end of that URL. For example for 'Web Booking

https://carrierconnect.etdatacenter.com/Default.aspx?accesstype=autologin&cust=id_015&user=templateuser

Where I currently have templateuser I need to put the value of the field ‘username’

thanks