Using , want to restrict access to file .wmv

Hi all,  I want to secure a particular set of files in a folder by role type.  I have the following entry (See below)...I notice this doesn't work (I.e., it doesn't secure the file by Role Type..anyone can access the file).  I've read that I need to map the .WMV extension to the ASp.Net DLL.  Can somebody give me some details on how to do that?  (I'm a newbie).
 
Thanks in advance.
 
<location path="media/mymediafile.wmv"> <system.web> <authorization> <allow roles="MediaRole" /> <deny users="*" /> </authorization> </system.web> </location>
 
 
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