Create a directory within a directory

Hello all.  I am loading a given directory into a dropdown.  Now I need to be able to select one of the folders in the dropdown, type ?whatever? in the the txtbox and create a folder inside that selected folded.  So if I select Windows2003 and type 10.5, when I open up the path it would read
C:\Apps\FTPsite\folders\Windows2003\10.5 
Here is my code I am currently using to create a directory and load the dropdown.
 
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load txtAdd.Focus() Page.Form.DefaultButton = btnFolder.UniqueID If Not Page.IsPostBack Then Dim dirInfo As New DirectoryInfo("C:\Apps\FTPsite\folders") ddOSFolder.DataSource = dirInfo.GetDirectories() ddOSFolder.DataBind() End If End Sub Protected Sub btnFolder_Click(ByVal sender As Object, B ...