To enable .flv files to play from IIS, all you need to do add a MIME type and below is how to doe this:
1) Open Internet Information Services (IIS) Manager
2) Right click on the computer name in the tree view to the left and select ‘Properties’
3) Click the ‘MIME Types’ button
4) Click the ‘New’ button
5) In the ‘Extension’ field enter ‘.flv’ (without the quotes)
6) In the ‘MIME type’ field enter ‘video/x-flv’ (without the quotes)
7) Click ‘OK
8) Click ‘OK
9) Click ‘OK’