In VBA Help look for information on "Drive Collection"
Here's the code supplied in the VBA Help file ... I've modified slightly to allow for drives that "aren't ready".
Sub ShowDriveList()
Dim fs, d, dc, s, n
Set fs = CreateObject("Scripting.FileSystemObject")
Set dc = fs.Drives
For Each d In dc
s = s & d.DriveLetter & " - "
If d.DriveType = Remote Then
On Error Resume Next
n = d.ShareName
Else
On Error Resume Next
n = d.VolumeName
End If
s = s & n & vbCrLf
Next
MsgBox s
End Sub