Enter this code in the declarations-section:
Declare Function GetLogicalDriveStrings Lib "kernel32" Alias "GetLogicalDriveStringsA" (Byval nBufferLength As Long, Byval lpBuffer As String) As Long
' Enter this code where You want to execute the check for available drives:
Dim tmp As String
Dim iCount As Integer
Dim strDrives As String
tmp = ""
strDrives = Space$(64)
Call GetLogicalDriveStrings(Len(strDrives), strDrives)
For iCount = 1 To Len(strDrives) Step 4
tmp = tmp & Mid$(strDrives, iCount, 1)
Next iCount
Msgbox tmp
Der Code gibt dir alle zur Verfügung stehenden Laufwerksbuchstaben aus.