You cannot force the client to use any particular application to open a file from the server: It all depends on the file associations that the client has currently set.
If you can run an application on the client (which you again, can't from the server) then you could set the file associations via the registry (there is an example here: http://stackoverflow.com/questions/69761/how-to-associate-a-file-extension-to-the-current-executable-in-c
]) but I woudl strongly not recommend it. I have a number of video programs, and some automatically change the file associations. Those are the programs I delete and never install again.