Downloading to a specific drive-Collection of common programming errors

My users must download a program from the interwebs to a microSD card, which can be any drive letter from A-Z.

Q: Is there a drop dead simple approach to downloading a file to a specified drive/directory without relying on the user to navigate for me? I can populate the directory with a seed file if necessary to let my program know the right home.

Example: FileName: This_is_it.txt (This let’s me know this is the right folder).

FileName: Program.prc (this is the program that I need the user to download and place into this folder).

I don’t know AIR yet, but I think AIR might be a solution, so that’s why I’m putting the AIR tag on this question.