Well, you just need to use the GetDirectories method of the DirectoryInfo object to get an array of all directories in the current directory. The you can just add to the listview calling GetFolderSize for each directory in the array, something like this:-
Public Sub LoadDirectoriesInListView(ByVal currentDirectoryValue As String)
ListView1.Items.Clear()
currentDirectory = currentDirectoryValue
Dim currentDirectoryInfo As DirectoryInfo = New DirectoryInfo(currentDirectory)
Dim directoryArray As DirectoryInfo() = currentDirectoryInfo.GetDirectories()
Dim dir As DirectoryInfo
For Each dir In directoryArray
Dim lvi As New ListViewItem(dir.Name)
lvi.SubItems.Add(GetFolderSize(dir.FullName, False))
ListView1.Items.Add(lvi)
Next
End Sub
Then you just call it like this:-
LoadDirectoriesInListView(currentDirectory)
Hope this helps