Here is an example to return all your drive letters.
Reqs.
1 textbox set to multi-line (txtAllDrives)
2 command buttons (cmdGetDrives and cmdClose)
VB Code:
  1. Option Explicit

  2.  
  3. Private Const DRIVE_UNKNOWN = 0

  4. Private Const DRIVE_ABSENT = 1

  5. Private Const DRIVE_REMOVABLE = 2

  6. Private Const DRIVE_FIXED = 3

  7. Private Const DRIVE_REMOTE = 4

  8. Private Const DRIVE_CDROM = 5

  9. Private Const DRIVE_RAMDISK = 6

  10. ' returns errors for UNC Path

  11. Private Const ERROR_BAD_DEVICE = 1200&

  12. Private Const ERROR_CONNECTION_UNAVAIL = 1201&

  13. Private Const ERROR_EXTENDED_ERROR = 1208&

  14. Private Const ERROR_MORE_DATA = 234

  15. Private Const ERROR_NOT_SUPPORTED = 50&

  16. Private Const ERROR_NO_NET_OR_BAD_PATH = 1203&

  17. Private Const ERROR_NO_NETWORK = 1222&

  18. Private Const ERROR_NOT_CONNECTED = 2250&

  19. Private Const NO_ERROR = 0

  20.  
  21. Private Declare Function WNetGetConnection Lib "mpr.dll" Alias "WNetGetConnectionA" (ByVal lpszLocalName As String, _

  22. ByVal lpszRemoteName As String, cbRemoteName As Long) As Long

  23.         

  24. Private Declare Function GetLogicalDriveStrings Lib "kernel32" Alias "GetLogicalDriveStringsA" (ByVal nBufferLength As Long, _

  25. ByVal lpBuffer As String) As Long

  26.     

  27. Private Declare Function GetDriveType Lib "kernel32" Alias "GetDriveTypeA" (ByVal nDrive As String) As Long

  28.     

  29. Private Function fGetDrives() As String

  30. 'Returns all mapped drives

  31.     Dim lngRet As Long

  32.     Dim strDrives As String * 255

  33.     Dim lngTmp As Long

  34.     lngTmp = Len(strDrives)

  35.     lngRet = GetLogicalDriveStrings(lngTmp, strDrives)

  36.     fGetDrives = Left(strDrives, lngRet)

  37. End Function

  38.  
  39. Private Function fGetUNCPath(strDriveLetter As String) As String

  40.  
  41.     On Local Error GoTo fGetUNCPath_Err

  42.  
  43.     Dim Msg As String, lngReturn As Long

  44.     Dim lpszLocalName As String

  45.     Dim lpszRemoteName As String

  46.     Dim cbRemoteName As Long

  47.     lpszLocalName = strDriveLetter

  48.     lpszRemoteName = String$(255, Chr$(32))

  49.     cbRemoteName = Len(lpszRemoteName)

  50.     lngReturn = WNetGetConnection(lpszLocalName, lpszRemoteName, cbRemoteName)

  51.     Select Case lngReturn

  52.         Case ERROR_BAD_DEVICE

  53.             Msg = "Error: Bad Device"

  54.         Case ERROR_CONNECTION_UNAVAIL

  55.             Msg = "Error: Connection Un-Available"

  56.         Case ERROR_EXTENDED_ERROR

  57.             Msg = "Error: Extended Error"

  58.         Case ERROR_MORE_DATA

  59.                Msg = "Error: More Data"

  60.         Case ERROR_NOT_SUPPORTED

  61.                Msg = "Error: Feature not Supported"

  62.         Case ERROR_NO_NET_OR_BAD_PATH

  63.                Msg = "Error: No Network Available or Bad Path"

  64.         Case ERROR_NO_NETWORK

  65.                Msg = "Error: No Network Available"

  66.         Case ERROR_NOT_CONNECTED

  67.                Msg = "Error: Not Connected"

  68.         Case NO_ERROR

  69.                ' all is successful...

  70.     End Select

  71.     If Len(Msg) Then

  72.         MsgBox Msg, vbInformation

  73.     Else

  74.         fGetUNCPath = Left$(lpszRemoteName, cbRemoteName)

  75.     End If

  76.     

  77. fGetUNCPath_End:

  78.     Exit Function

  79.     

  80. fGetUNCPath_Err:

  81.     MsgBox Err.Description, vbInformation

  82.     Resume fGetUNCPath_End

  83.     

  84. End Function

  85.  
  86. Private Function fDriveType(strDriveName As String) As String

  87.  
  88.     Dim lngRet As Long

  89.     Dim strDrive As String

  90.     

  91.     lngRet = GetDriveType(strDriveName)

  92.     Select Case lngRet

  93.         Case DRIVE_UNKNOWN 'The drive type cannot be determined.

  94.             strDrive = "Unknown Drive Type"

  95.         Case DRIVE_ABSENT 'The root directory does not exist.

  96.             strDrive = "Drive does not exist"

  97.         Case DRIVE_REMOVABLE 'The drive can be removed from the drive.

  98.             strDrive = "Removable Media"

  99.         Case DRIVE_FIXED 'The disk cannot be removed from the drive.

  100.             strDrive = "Fixed Drive"

  101.         Case DRIVE_REMOTE  'The drive is a remote (network) drive.

  102.             strDrive = "Network Drive"

  103.         Case DRIVE_CDROM 'The drive is a CD-ROM drive.

  104.             strDrive = "CD Rom"

  105.         Case DRIVE_RAMDISK 'The drive is a RAM disk.

  106.             strDrive = "Ram Disk"

  107.     End Select

  108.     fDriveType = strDrive

  109.     

  110. End Function

  111.  
  112. Sub sListAllDrives()

  113.  
  114.     Dim strAllDrives As String

  115.     Dim strTmp As String

  116.     

  117.     strAllDrives = fGetDrives

  118.     If strAllDrives <> "" Then

  119.         Do

  120.             strTmp = Mid$(strAllDrives, 1, InStr(strAllDrives, vbNullChar) - 1)

  121.             strAllDrives = Mid$(strAllDrives, InStr(strAllDrives, vbNullChar) + 1)

  122.             Select Case fDriveType(strTmp)

  123.                 Case "Removable Media":

  124.                     txtAllDrives = txtAllDrives & "Removable drive : " & strTmp & vbNewLine

  125.                 Case "CD Rom":

  126.                     txtAllDrives = txtAllDrives & " CD Rom drive : " & strTmp & vbNewLine

  127.                 Case "Fixed Drive":

  128.                     txtAllDrives = txtAllDrives & " Local drive : " & strTmp & vbNewLine

  129.                 Case "Network Drive":

  130.                     txtAllDrives = txtAllDrives & " Network drive : " & strTmp & vbNewLine

  131.                     txtAllDrives = txtAllDrives & " UNC Path : " & _

  132.                                 fGetUNCPath(Left$(strTmp, Len(strTmp) - 1)) & vbNewLine

  133.             End Select

  134.         Loop While strAllDrives <> ""

  135.     End If

  136. End Sub

  137.  
  138. Private Sub cmdClose_Click()

  139.     Unload Me

  140. End Sub

  141.  
  142. Private Sub cmdGetDrives_Click()

  143.     txtAllDrives = "All available drives: " & vbNewLine & vbNewLine

  144.     sListAllDrives

  145. End Sub