You may not have the talent to make a game like Portal 2, but Valve's not going to stop you from trying. The company released a beta version of their Portal 2 "Authoring Tools" last night, the same software used to produce the very levels you've been playing the last few weeks.
The news was announced on Valve's official Portal 2 blog, where Valve asked its community testers to submit any bugs they come across--the tools are not final. If you'd like to download the Authoring Tools for yourself, click over to the "Tools" tab in Steam.
More details, including some helpful mailing lists to keep tabs on, are available on the blog.
The tools are also, at the moment, Windows only. I've contacted Valve about possible Mac support.