Install .NET 1.1 and all service packs if not on the OS already.
Open the IIS Manager and navigate to the server root. (Not a website root, above that - the machine name.)
Double-click "ISAPI and CGI restrictions."
Add the v1.1 aspnet_isapi.dll to "Allowed" restrictions (it'll be at %Windows%\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll)
Navigate to the website root in IIS manager and double-click "ISAPI Filters."
Add the ASP.NET 1.1 ISAPI filter from %Windows%\Microsoft.NET\Framework\v1.1.4322\aspnet_filter.dll
Go to the website root again in IIS manager and look at "Advanced Settings."
Ensure the website is using an ASP.NET 1.1 Application Pool (Vista created one for me when I installed .NET 1.1 - you may need to create one yourself.)
