How to use .dll extension on IIS?

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I have to develop an application (woeking on IIS) witch have to accept input
string through HTTP protocol. Client sends request: "GET
/Test/Test.dll?list_o f_parameters... ". I can't change this string on client
side. How to tell IIS (on XP Pro SP3) to accept this data and call some other
proccess to use this. How IIS can open a *.dll page?