IIS Q: How can I configure IIS executable extensions & custerr?

Please don't blame this question and I would be grateful if you can give me a specific answer.

I'm using Windows Server 2008 6.0 x86 with MsSQL 08.

1. I want to limit the extension of IIS executable files on my web server.

ex:)

Before set limit.

Executable extension : *.asp | *.aspx ...

After set limit.

Executable extension : only *.asp

I don't know exactly what the Handler Mappings menu is.

2. How to set 404 custerr when I call specified file?

Test file on 'C:\inetpu\wwwroot\main\test.browser'.

When I call this file on browser, it returns 404.7

The request filtering module is configured to deny the file extension.

Why this happens? is there any way to see the content of 'test.browser'? or is it impossible?

Someone please help me. Thank you in advance.