ASP.NET is an add on. It's not 100% clear from the signup page, but the comparison page shows all the correct information.
http://x10hosting.com/free-hosting-comparison
I'm sorry for the confusion. The administrators of X10Hosting had to disabled this feature very quickly to curb issues that had come from ASP.NET. I'm not sure why the page still shows it in a potentially misleading way, but the administrators have been notified of the situation.
Personally, I would find a Windows host and not a Linux host for ASP.NET. Unless you're using version 2.0, your application will not be supported by ANY Linux host.