Listing Folders in Dropdown menu

Anybody knows how to list folders in dropdown menu. I wanna list all the main folders in one dropdwon menu. When user select a particular folder from the dropdown menu, in the second dropdown menu the sub folders of the main folder should automatically populate in the dropdown. Can anyone help me out in the problem.

Sorry about the format - i'm limited to 4000 chars and this function is actually larger than that - but it'll give you the concept.
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<!--#include virtual="/new/common/utils/qsort.asp" -->
<%
'
' DirFilestoOptions(DirName, SortOrder)
' DirName = name of relative path from curent file to generate options from
' SortOrder = True (ascending), False (descending)
'
' This subroutine takes a relative path spec., gets a list of files from it, sorts the
' list of files, and then outputs options as part of a <select> tag in a form.
' The option value=<x> will be set to point to the relative URL for the files.
' All date related names will be translated to Month and Year for display purposes
' if filelimit is specified, the files will be limited
'
sub DirFilestoOptions(DirName, FileLimit, LimitCompare, SortOrder)

dim FileSysObj, DirObj, fname, flink, tmp, fpath, fileobj, pos, npos, skipfile, iStart, iEnd, iStep

set FileSysObj=Server.CreateObject("Scripting.FileSystemObject")
fpath=server.MapPath(DirName)
set DirObj = FileSysObj.GetFolder(fpath)
if (isempty(DirObj)) then
response.write("<option value=""#"">Internal File Structure Error</option>")
else
dim I
I = DirObj.files.count
dim filelist()
redim filelist(I)
I=1
for each fileobj in DirObj.files
filelist(I) = fileobj.name
I=I+1
next
%> <script language="VB">
QSort(filelist, 1, DirObj.files.count)
</script>
<%
if SortOrder then
iStart = 1
iEnd = DirObj.files.count
iStep = 1
else
istart = DirObj.files.count
iend = 1
iStep = -1
end if
for I = iStart to iEnd step iStep
fname=lcase(filelist(I))
flink= DirName & "/" & fname
response.write("<option value=""" & flink & """>" & fname & "</option>")
next
end if
end sub
%>