Create folder in temp directory

[jack1234]

Considered the following code:

Private Declare Function GetTempPath Lib "kernel32" Alias "GetTempPathA" _
                (ByVal nBufferLength As Long, _
                ByVal lpBuffer As String) As Long
Private Declare Function GetTempFileName Lib "kernel32" Alias "GetTempFileNameA" (ByVal lpszPath As String, ByVal lpPrefixString As String, ByVal wUnique As Long, ByVal lpTempFileName As String) As Long

Public Function GetTempDir() As String
    Dim sBuffer As String
    Dim lRetVal As Long

    sBuffer = String(255, vbNullChar)

    lRetVal = GetTempPath(Len(sBuffer), sBuffer)

    If lRetVal Then
        GetTempDir = Left$(sBuffer, lRetVal)
    End If
End Function

Private Sub Command1_Click()
Dim sBuffer As String
 sBuffer = String$(255, vbNullChar)
GetTempFileName GetTempDir(), "aaa", 0, sBuffer
MsgBox sBuffer

End Sub

My question is:
1)Does the code above guarantee to generate a unique filename?
2)This code can only generate file with .tmp extension in user temp directory, how to create a folder with unique name?