Hi Benjamin,

I am a .NET Developer specialising in Web Development. The only stuff a browser natively understands is HTML and client scripts (Javascript & VBScript). ASP.NET and PHP are technologies that generated the HTML and scripts on the web server and then send them to the browser to be rendered. Most data-driven web sites are based on server side generation of HTML. ASP.NET is a platform developed by Microsoft to develop Web Applications in .NET. It's the most productive platform, but has a high learning curve and requires a Microsoft Windows Server and IIS to be installed. PHP is the open source alternative. It's free and there are a lot of people out there using it. PHP can be used with Apache Server which is also free and runs on any operating system I know. There is also a project called Mono that copies Microsoft .NET (including ASP.NET), so that you can develop in and run your .NET apps on *nix (Linux, Unix...).
You'll need to use a lot of client script to create a interactive web application (i.e. your games site) or you might use AJAX, but that won't be easy. Most useful web games I have seen so far were implemented as Java Applets, because it's performant and you can pretty much do anything with it. Hope this helps.

(Of course, copying this text to my clipboard, before submitting it ;-))