Put this in a file.vbs and add it to your Task Scheduler.
sLogFolder = "c:\inetpub\logs\LogFiles"
iMaxAge = 7
Set objFSO = CreateObject("Scripting.FileSystemObject")
set colFolder = objFSO.GetFolder(sLogFolder)
For Each colSubFolder in colFolder.SubFolders
Set objFolder = objFSO.GetFolder(colSubfolder.Path)
Set colFiles = objFolder.Files
For Each objFile in colFiles
iFileAge = now-objFile.DateCreated
if iFileAge > (iMaxAge+1) then
objFSO.deletefile objFile, True
end if
Next
Next