how to allow user to navigate through subdirectories, select, and download files

Hello,
I have been googling and reading for days but cannot find a way to  allow user to select from the contents of a number of subdirectories and download a file.  I've seen how to download a file from within one directory, as well as displaying the files in  a grid but I am unable to find a way to diplay the directory tree and allow the user to navigate to a subsirectory, select a file, and then download it.
I have version 2.0 of ASP.NET and I use VB.  Can someone point me in the right direction?
Thanks!
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