Both Get or Post method will work for you. Not sure where you start to 'post' the information, the Flash? or the HTML that hosting the Flash?
1. you should have a dynamic page working on your site, php or jsp.
2. you can use Get method to 'post' those tracked informations, something like this:
http://yourdomain.com/trackdata?Cust...,music2,music3
3. the trackdata is a php or jsp page, when open it, it starts working..to record those informations to your database... CustID=111&MostPlayed=music1,music2,music3
4. then sure, you can simply ouput a OK to the caller.. Flash, or HTML.
5. yes. when using AJAX, your customer will not know anything when you send out those informations...