Hola:
Probe con esto pero no funciona
Código PHP:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Documento sin título</title>
</head>
<body><form action="" method="post">
<input name="nombreid" type="text" />
<input name="" type="button" onclick="location.href = "http://www.mercantil.com/SE/Results.asp?wordstype=ALL&optArea=ALL&optsearchby=mecolegalname&chkiesearchby=ALL&chkNewsSearchBy=t&chkProdSearchBy=prodnameesp&chkBOSField=ALL&chkBOSType=ALL&chkJobField=TIT&keywords=" + document.getElementById("nombreid").value + "&Countrychk=1&optCategory=companies""; /></form>
</body>
</html>