Adding security to perticular folder.

Hello friends.
 
I have developed my site in ASP.NET,C# ,SQL Server 2005.Now i have a pre developed html site with 20 to 30 pages.which is working fine.
Now i want to include that folder to my website.i have uploaded it in my web site's root folder.But i want to provide security to that folder. Suppose if user has not logged in than he can not access those html pages.So can i do that??How can i give security to that particular folder??it contains only HTML pages.
The file structure of my web site is,
Mysite
--AppCode 
--Bin
-- Admin
--Folder(this is the folder of html pages.) 
--Default.aspx
web.config
 
Any idea about it???????? 
 
 
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