Okay, so I've definitely written my fair share of HTTP Handlers in ASP.NET (i.e., the classes that inherit from IHttpHandler), and when I found out that my website host doesn't support modifying the web.config to allow HttpHandlers made me very upset. Especially when I implemented the Blogger API on my website and wanted to use a free desktop publishing tool (that I'm using now). Anyway, I had given up on using an HttpHandler to implement the XMLRPC method calls the Blogger API uses. I was reading up on something and noticed an ASHX file extension. Did a quick google search and found out that's the OTHER way to create an HttpHandler. I fired up Visual Studio, created an ASHX file, made it inherit my old XmlRpc class and voila! it worked perfectly!
Useful to know if you can't modify the web.config file.