Secure downloadable files?

I would think your best bet would be to store the files you want downloadable at an online free service like Mediafire of Snapfiles (why use your own domain for storage and bandwidth, right?). You can password any files there, so only those who know the password could get them even with an open link.

It’s then simple enough to put a plain html link in your sidebar to your download folder/s. Click the link – you’re at the download folder. Select file/s, enter password, voila.