This is not something you can do from the web page. The server extensions
also have nothing to do with this. What happens is:
Browser Requests MP3 file from server
Server sends a MIME header telling information about the file and sends the
file
Browser reads the MIME header and tries to determine what application to
open the file with.
Unfortunately, there's nothing you can do in HTML that will tell Vista what
to do. It could be that there is a problem in Vista itself, or it could be
just with that installation of Vista as sometimes a program can confuse the
file associations within an OS. Check that it doesn't work on another Vista
computer as well so you can narrow down if it's one Vista computer or not,
but other than that there's nothing you can do to tell how a file should be
opened from HTML.
Hope this helps,
Mark Fitzpatrick
Microsoft MVP- Expression