I do something similar.  I use a sloppy piece of code that displays filenames in a folder for the links and I really don't want to distribute it because it's so poorly written, but basically it reads the file names in the folder, truncates the extension and displays them as a link to the files.  I use the same code for a different folder that is the "archived" files, basically anyting more than 90 days old.  And I use a nightly VBS script that moves anything with a file date over 90 days old from one folder to the other.  It ain't pretty, but it accomplishes the task.

You can pretty much do the same with DNN's Documents or Repository module, either with code or simply manually moving files older than a certain time frame.

Jeff