Validar si el usuario existe

[jahman]

Que tal como estan espero que bien y que alguien me pueda ayudar el problema que tengo es tratar de cuando un usuario se registra y existe el username que eligio mostrar un mensaje o por ultimo no dejar que se registre bajo el mis mo username, GRACIAS y espero que alguien me pueda ayudar

DISCULPE POR NO COLOCARLO CON CODIGO PERO EL OPERA NO ME ABRE LA VENTANITA
<%
Dim usuarios
Dim usuarios_numRows
Set usuarios = Server.CreateObject("ADODB.Recordset")
usuarios.ActiveConnection = MM_acceso_STRING
usuarios.Source = "SELECT * FROM usuarios "
usuarios.CursorType = 0
usuarios.CursorLocation = 2
usuarios.LockType = 1
usuarios.Open()

usuarios_numRows = 0
' *** Declaro variables

Dim MM_editAction
Dim MM_abortEdit
Dim MM_editQuery
Dim MM_editCmd

Dim MM_editConnection
Dim MM_editTable
Dim MM_editRedirectUrl
Dim MM_editColumn
Dim MM_recordId

Dim MM_fieldsStr
Dim MM_columnsStr
Dim MM_fields
Dim MM_columns
Dim MM_typeArray
Dim MM_formVal
Dim MM_delim
Dim MM_altVal
Dim MM_emptyVal
Dim MM_i

MM_editAction = CStr(Request.ServerVariables("SCRIPT_NAME"))
If (Request.QueryString <> "") Then
MM_editAction = MM_editAction & "?" & Request.QueryString
End If


MM_abortEdit = false


MM_editQuery = ""
%>
<%


If (CStr(Request("MM_insert")) = "form1") Then

MM_editConnection = MM_acceso_STRING
MM_editTable = "usuarios_alma"
MM_editRedirectUrl = "ok.asp"
MM_fieldsStr = "nombre|value|apellido_pat|value|apellido_mat|valu e|email|value|rut|value|dig|value|plataforma|value |login|value|username|value|password|value|pregunt a_secreta|value|respuesta|value"
MM_columnsStr = "nombre|',none,''|apellido_pat|',none,''|apellido_ mat|',none,''|email|',none,''|rut|',none,''|dig|', none,''|plataforma|',none,''|login|',none,''|usern ame|',none,''|password|',none,''|pregunta_secreta| ',none,''|respuesta|',none,''"


MM_fields = Split(MM_fieldsStr, "|")
MM_columns = Split(MM_columnsStr, "|")


For MM_i = LBound(MM_fields) To UBound(MM_fields) Step 2
MM_fields(MM_i+1) = CStr(Request.Form(MM_fields(MM_i)))
Next


If (MM_editRedirectUrl <> "" And Request.QueryString <> "") Then
If (InStr(1, MM_editRedirectUrl, "?", vbTextCompare) = 0 And Request.QueryString <> "") Then
MM_editRedirectUrl = MM_editRedirectUrl & "?" & Request.QueryString
Else
MM_editRedirectUrl = MM_editRedirectUrl & "&" & Request.QueryString
End If
End If

End If
%>

<%


Dim MM_tableValues
Dim MM_dbValues


'*** es aca donde tengo el problema, recogo el dato del formulario lo guardo en una variable hago un loop para buscar entre todos los registro si ya existe uno ya registrado pero aun lo guarda***'

MM_valUsername=CStr(Request.Form("username"))
While ((Repeat__numRows <> 0) AND (NOT usuarios.EOF))
IF usuarios.Fields("username") <> MM_valUsername

If (CStr(Request("MM_insert")) <> "") Then
MM_tableValues = ""
MM_dbValues = ""
For MM_i = LBound(MM_fields) To UBound(MM_fields) Step 2
MM_formVal = MM_fields(MM_i+1)
MM_typeArray = Split(MM_columns(MM_i+1),",")
MM_delim = MM_typeArray(0)
If (MM_delim = "none") Then MM_delim = ""
MM_altVal = MM_typeArray(1)
If (MM_altVal = "none") Then MM_altVal = ""
MM_emptyVal = MM_typeArray(2)
If (MM_emptyVal = "none") Then MM_emptyVal = ""
If (MM_formVal = "") Then
MM_formVal = MM_emptyVal
Else
If (MM_altVal <> "") Then
MM_formVal = MM_altVal
ElseIf (MM_delim = "'") Then ' escape quotes
MM_formVal = "'" & Replace(MM_formVal,"'","''") & "'"
Else
MM_formVal = MM_delim + MM_formVal + MM_delim
End If
End If
If (MM_i <> LBound(MM_fields)) Then
MM_tableValues = MM_tableValues & ","
MM_dbValues = MM_dbValues & ","
End If
MM_tableValues = MM_tableValues & MM_columns(MM_i)
MM_dbValues = MM_dbValues & MM_formVal
Next
MM_editQuery = "insert into " & MM_editTable & " (" & MM_tableValues & ") values (" & MM_dbValues & ")"

If (Not MM_abortEdit) Then
' execute the insert
Set MM_editCmd = Server.CreateObject("ADODB.Command")
MM_editCmd.ActiveConnection = MM_editConnection
MM_editCmd.CommandText = MM_editQuery
MM_editCmd.Execute
MM_editCmd.ActiveConnection.Close

If (MM_editRedirectUrl <> "") Then
Response.Redirect(MM_editRedirectUrl)
End If
End If
End If
Repeat__numRows = 0
ELSE
Repeat__index=Repeat__index+1
Repeat__numRows=Repeat__numRows-1
END IF
usuarios.MoveNext()
Wend