I can't comment to much on asp specificaly, but you can use almost any server side scripting language to create an xml file. I have done this in the past using php. What I did was create a file called feed.xml this file was in fact a php file with an xml file extension. I was then able to set up the server so that xml was handled in the same way php would be.
When a request was made for feed.xml the php file did its stuff, queried the database and created the output. To the browser or application that was requesting feed.xml they just saw xml output. If you set up your script to create xml style output, and have an xml extenson to the end user/applicaion it will be as good as a true xml file.