HTML - input & select to URL - url

Question

I would like my clients to add in there URL, plus select from a drop down to complete the URL, going to a new page on clicking a button.
<form name="form1" method="post" action="">
<label>http://www.
<input type="text" name="input1" id="input1" value="mydomain.com">
</label>
/
<select name="select" id="select">
<option value="Select" selected>Select</option>
<option value="cPanel">cPanel</option>
<option value="Webmail">Webmail</option>
</select>
<label>
<input type="submit" name="button1" id="button1" value="Submit">
</label>
</form>
What must still be added to the above simple html code, (which is just the format), so my clients just need to add there domain, select an option from the drop down and click submit to take them to there respective login screen. The link will be typically:
http://example.com/cpanel or http://example.com/webmail

Answer 1

I received this fine answer from Chris on Yahoo Answers, thought I would share the answer.
http://jsfiddle.net/khrismuc/gwM9K/
<form onsubmit="return go(this.where.value, this.which.value)">
http://
<input type="text" name="where" id="input1" value="www.mydomain.com" />/
<select name="which" id="select">
<option value="Select">Select</option>
<option value="cPanel">cPanel</option>
<option value="Webmail">Webmail</option>
</select>
<input type="submit" name="button1" id="button1" value="Submit" />
</form>
// https://answers.yahoo.com/question/index?qid=20140327005411AAk9zW1
// form -> go to url
var go = function(where, which) {
if (which === "Select") return false;
// change option to url part
if (which === "cPanel") which = "cpanel";
if (which === "Webmail") which = "webmail";
document.location.href = "http://" + where + "/" + which;
return false;
};