Vista - Copy Application Event Logs For Past 30 Days To XLS

The script below works great; however, I'm having trouble getting the
30 day portion of the script working. Any help would be greatly
appreciated. Thanks in advance for your help...

On Error Resume Next
strComputer = "."
strFile = "C:\Application Event Logs.xls"

Set objWMIService = GetObject("winmgmts:" _
& "{impersonationLevel=impersonate,(Security)}!\\" & _
strComputer & "\root\cimv2")

Set colLoggedEvents = objWMIService.ExecQuery _
("Select * From Win32_NTLogEvent Where Logfile = 'Application'")

'EventType Value = Meaning
' 1 = Error
' 2 = Warning
' 3 = Information
' 4 = Security Success
' 5 = Security Failure
' 8 = Security audit success
' 16 = Security audit failure

Set objExcel = CreateObject("Excel.Application")
objExcel.Visible = False
objExcel.Workbooks.Add
objExcel.Cells(1,1).Value = "System Event log Errors+Warnings for " &
strComputer
objExcel.Cells(1,1).Font.Bold = True
objExcel.Cells(1,1).Font.Size = 13
objExcel.Cells(1,1).Interior.ColorIndex = 11
objExcel.Cells(1,1).Interior.Pattern = 1 'xlSolid
objExcel.Cells(1,1).Font.ColorIndex = 2
objExcel.Cells(1,1).Borders.LineStyle = 1 '= xlSolid
objExcel.Cells(1,1).WrapText = True

objExcel.Cells(2,1).Value = "Time: " & Now
objExcel.Cells(2,1).Font.Bold = True
objExcel.Cells(2,1).Font.Size = 12
objExcel.Cells(2,1).Interior.ColorIndex = 11
objExcel.Cells(2,1).Interior.Pattern = 1 'xlSolid
objExcel.Cells(2,1).Font.ColorIndex = 2
objExcel.Cells(2,1).Borders.LineStyle = 1 '= xlSolid
objExcel.Cells(2,1).WrapText = True

objExcel.Cells(4,1).Value = "Time Generated"
objExcel.Cells(4,1).Font.Bold = True
objExcel.Cells(4,1).Font.Size = 11
objExcel.Cells(4,2).Value = "LogFile"
objExcel.Cells(4,2).Font.Bold = True
objExcel.Cells(4,2).Font.Size = 11
objExcel.Cells(4,3).Value = "Type"
objExcel.Cells(4,3).Font.Bold = True
objExcel.Cells(4,3).Font.Size = 11
objExcel.Cells(4,4).Value = "Event Code"
objExcel.Cells(4,4).Font.Bold = True
objExcel.Cells(4,4).Font.Size = 11
objExcel.Cells(4,5).Value = "Message"
objExcel.Cells(4,5).Font.Bold = True
objExcel.Cells(4,5).Font.Size = 11

x = 5
y = 1

For Each objEvent in colLoggedEvents

If objEvent.Type="error" or objEvent.Type="warning" Then

strTimeGen = (evtdatetime(objEvent.TimeGenerated))
strLogfile = objEvent.Logfile
strType = objEvent.Type
strEventCode = objEvent.EventCode
srtMessage = Trim( Replace( objEvent.Message, vbCrLf, " "))

y1 = y
objExcel.Cells(x,y1).Value = strTimeGen
y1 = y1 + 1
objExcel.Cells(x,y1).Value = strLogfile
y1 = y1 + 1
objExcel.Cells(x,y1).Value = strType
y1 = y1 + 1
objExcel.Cells(x,y1).Value = strEventCode
y1 = y1 + 1
objExcel.Cells(x,y1).Value = srtMessage

x = x + 1

End If
Next

objExcel.Columns("A:E").Select
objExcel.Selection.HorizontalAlignment = 1 'xlLeft
objExcel.Selection.Borders.LineStyle = 1 '= xlSolid

objExcel.Range("A1","E1").MergeCells = 1
objExcel.Range("A2","E2").MergeCells = 1

objExcel.Columns("A:AH").EntireColumn.AutoFit

objExcel.DisplayAlerts = False
Set objWorkbook = objExcel.ActiveWorkbook
objWorkbook.SaveAs strFile
objWorkbook.Close
objExcel.Quit

msgbox "Application Export Complete!"

Function evtdatetime(evttime)
Dim tmGen, dtPart,tmPart
tmGen = Left(evttime,14)
dtPart = Left(tmGen,8)
tmPart = Right(tmGen,6)
evtdatetime = Left(dtPart,4) & "/" & Mid(dtPart,5,2) & "/" & Right
(dtPart,2) &","& _
Left(tmPart,2) & ":" & Mid(tmPart,3,2) & ":" & Right(tmPart,2)
End Function