Check-out web-based file and download to specific client filesystem location

I am trying to accomplish web-based file check-out / check-in capability where files on the server can be checked-out and downloaded to a specific location in the client filesystem, edited and then uploaded.  I've been able to accomplish just about all of the steps using HTML5 and FreeASPUpload, but am hitting a wall in the ability to download from the web-server to a specific location on the client filesystem.  I need to support Chrome, Firefox, IE and Safari.

Does anyone have any code samples, links or reccomendations on how to write a downloaded files to a specific location in the client filesystem?  I don't have a problem is they have to go through a one-time client setup or if it requires some level of trust relationship.  I just need to keep it simple so the relative path on the client mimics the relative path on the server so clients can find the files they downloaded and so we can direct them to the correct client file when it comes time to upload and check-in once they complete edits.

Thanks!