I use this: http://www.wimpyplayer.com/

There isn't any special ASP.Net code for embedding it like an image. There's
a short tutorial over at:
http://www.tizag.com/flashTutorial/flashhtmlcode.php  That goes through
pretty much all you should need to know.

If you're looking for components to do the job, or want to use flash more
thoroughly later, there are a couple nice controls out there

DevExpress (www.devexpress.com) has a control as part of their asp.net
utilities called the ASPxObjectContainer that can embed flash and other
media items (http://www.devexpress.com/Products/NET/WebForms/ASPxUtilities/)
I've used it and it's nice and simple.

There's also http://www.flash-control.net/?gclid=CLijnM24spECFQMmIgodyxC_Nw,
but I haven't used that one myself.

http://www.aspnetflash.com/ also has a good suite of media components
including a very good flash control.

Feel free to use this free Flash ASP.NET Web Control I put together or read
about how it works and do it yourself:
http://SteveOrr.net/articles/Flasher.aspx