ASP and ASP.NET are NOT! the same thing. Some people enable ASP.NET hoping that ASP will work also, this is just not the case. IIS 6.0 comes with ASP disabled by default, and this will show you how to enable it.
Load IIS from the Administrative tools in the Control Panel by clicking Start -> Administrative Tools -> IIS Manager (or loading the Control Panel, entering the Administrative Tools folder, and double clicking IIS Manager).
Go to the Web Service Extensions tab, click Active Server Pages, then press the "Allow" button on the left
Your ASP pages should now work :-)