I'm pretty sure I already know the answer to this, as being able to force the client's computer to open a file with the "Webserver chosen application" would be a huge security risk, but I'm going to ask it anyways.
Can you force an end user's computer to open a file using a certain program? For example, can I use my server to tell a client computer "You need to open *.reg files with Media Player"?
Some background is that we have this website that recently got revamped; it moved from Rails to Drupal, and now the client is saying that when she downloads a .reg file on her website, it tries to open it in Windows Media Player. She says that this didn't happen until we switched websites, so they blame it on the website, but I thought it wasn't possible to set the associated application with the download. I know the file hasn't changed because when I download it and look at it, it indeed is a Registry file.