Dim f As FolderItem
f=getfolderitem("pathToMyFolder")

Dim filetype() As String
filetype = Array(".txt",".rtf")

Dim fileext As String

Dim i As Integer

dim fileList() as FolderItem

dim folderCount as integer = f.Count

for i = 1 to folderCount
  fileList.Append f.Item( i )
next
for i = 0 to fileList.Ubound
  dim thisFile as FolderItem = fileList( i )
  dim thisName as string = thisFile.Name
  For Each fileext In filetype
    dim thisExt as string = thisName.Right( fileext.Len )
    if thisExt = fileext then
      ListBox1.AddRow thisName
    end if
  next
next