Hola choroy.
Aca está un modelo, pruébalo.
Código PHP:
<html>
<head>
<script language="JavaScript">
function verifica(){
var todoOk = false;
with (document.frm){
todoOk = todoOk || (check1.checked);
todoOk = todoOk || (check2.checked);
todoOk = todoOk || (check3.checked);
todoOk = todoOk || (check4.checked);
todoOk = todoOk || (check5.checked);
}
if (!todoOk)
alert("Debes seleccionar al menos un destinatario");
else
document.frm.submit();
}
</script>
</head>
<body>
<form name="frm">
<table border="0">
<tr>
<td>
<input type="checkbox" name="check1">
</td>
<td>
[email][email protected][/email]
</td>
</tr>
<tr>
<td>
<input type="checkbox" name="check2">
</td>
<td>
[email][email protected][/email]
</td>
</tr>
<tr>
<td>
<input type="checkbox" name="check3">
</td>
<td>
[email][email protected][/email]
</td>
</tr>
<tr>
<td>
<input type="checkbox" name="check4">
</td>
<td>
[email][email protected][/email]
</td>
</tr>
<tr>
<td>
<input type="checkbox" name="check5">
</td>
<td>
[email][email protected][/email]
</td>
</tr>
<tr>
<td colspan="2" align="center">
<input type="button" name="envia" value="Enviar" onclick="verifica()">
</td>
</tr>
</table>
</form>
</body>
</html>
Saludos.