f$ = "C:\WINDOWS"
dirFolder = Dir(f$, vbDirectory)
If dirFolder <> "" Then
    strmsg = MsgBox("This folder already exists.", vbCritical)
    'directory exists action here
End If

Public Function FileExists(strPath As String) As Integer 
    FileExists = Not (Dir(strPath) = "")
End Function

Dim FileSize As Long
FileSize& = FileLen("C:\SOMEFILE.TXT")
msgbox filesize& & " bytes"