This any good? :-

Const mcsBasePath = "g:\temp\"

Dim mfso: Set mfso = CreateObject("Scripting.FileSystemObject")
Dim moDOM: Set moDOM = Nothing
Dim msPath: msPath = ""

Class CPayment
 Public ReceiptType
 Public ReceiptMethod
 Public ReceiptRef
 Public ReceivedFrom
 Public AccountNumber
 Public Amount
 Public BankAccountID
 Public DeclineReinstatement
End Class

' Input Loop code here
' Creates a CPayment object with Set oPayment = New CPayment
' populates it with data
' Calls AddPayment with the Batch number and the instance of oPayment as
parameters

If Not moDOM is Nothing Then moDOM.save msPath

Function AddPayment(Batch, Payment)

Dim rootEl, paymentEl

Set rootEl = GetRootForBatch(Batch)

Set paymentEl = AddElem(rootEl, "Payment")

AddElem paymentEl, "ReceiptType", Payment.ReceiptType
AddElem paymentEl, "ReceiptMethod", Payment.ReceiptMethod
AddElem paymentEl, "ReceiptRef", Payment.ReceiptRef
AddElem paymentEl, "ReceivedFrom", Payment.ReceivedFrom
AddElem paymentEl, "AccountNumber", Payment.AccountNumber
AddElem paymentEl, "Amount", Payment.Amount
AddElem paymentEl, "BankAccountID", Payment.BankAccountID
AddElem paymentEl, "DeclineReinstatement", Payment.DeclineReinstatement

End Function


Function GetRootForBatch(Batch)
 Dim sPath, p

 sPath = mcsBasePath & Batch & ".xml"

 If sPath <> msPath Then

  If Not moDOM is Nothing Then
   moDOM.save msPath
  End If

  Set moDOM = CreateObject("MSXML2.DOMDocument.3.0")

  If gfso.FileExists(sPath) Then
   moDOM.load(sPath)
  Else
   moDOM.loadXML("<ImportPayments />")
   Set p = moDOM.createProcessingInstruction("xml", "version='1.0'")
   moDOM.insertBefore p, moDOM.documentElement
  End If

  msPath = sPath
 End If

 Set GetRootForBatch = moDOM.documentElement

End Function

Function AddElem(parent, name, value)

Set AddElem = parent.ownerDocument.createElement(name)
If Not IsNull(value) AddElem.text = value

End Function