The code is :

<%@ LANGUAGE="VBSCRIPT" %>
<%
	Option Explicit
	Response.Buffer=1
	
	Dim newID
	Dim cnn
	Dim rs
	Set cnn = Server.CreateObject("ADODB.Connection")
	Set rs = Server.CreateObject("ADODB.Recordset")
	cnn.ConnectionString = Application("ConnectionString")
	cnn.Open
	
	rs.Open "prestaciones", cnn, 2, 3, 2
	If rs.EOF Then 
		newID = 1
	Else
		rs.MoveLast
		newID = rs("id") + 1
	End If
	
	rs.AddNew
	
	rs("ID") = newID
	rs("APELLIDO") = Trim(Request("apellido"))
	rs("NOMBRE") = Trim(Request("nombre"))
	rs("STAFF") = Trim(Request("staff"))
	rs("APENOM") = UCase( Left(Request("apellido"),3) & Left(Request("nombre"),3) )
	rs("FECPED") = CDate(Request("fecped"))
	rs("ICD10DIAGNOS") = Trim(Request("icd10"))
	rs("DIAGNOSTICO") = Trim(Request("diagnostico"))
	rs("ID_PRAC") = CLng(Request("id_prac"))
	rs("PRACTICA") = Trim(Request("practica"))
	rs("FECAUT") = Null
	rs("FECREC") = Null
	rs("FECREAL") = Null
	rs("OBSERVA") = Trim(Request("observa"))
	rs("NOTAS") = Null
	rs("ID_INST") = Session("id_inst")
	rs("INSTITUTO") = Session("nombre")
	rs("ID_MED") = CLng(Request("id_med"))
	rs("MEDICO") = Trim(Request("medico"))

	rs.Update
		
	rs.Close
	Set rs = Nothing
	cnn.Close
	Set cnn = Nothing

	Response.Clear
	Response.Redirect "pedidoaceptado.asp?id="&newID
%>

A question to Cetin's answer: What about empty dates??
Thanks all for your reply