On the Windows 2003 server, open the Internet Information Services Manager. 

Expand the Local Computer Server. 

Right-click the local computer server and select Properties. 

Select the MIME Types tab. 
Click the New... button and enter the following information: 

Associated Extension box: .FLV 
MIME Type box: flv-application/octet-stream 

Click Ok. 
Restart the World Wide Web Publishing service.