A fundamental misconception about the Media Lab is that it is an engineering lab. Yes, the technologies that are developed are forward-thinking enough that most students and professors there must be at least moderately skilled engineers. However, the primary goal of the media lab is to birth new ideas, not new implementations.

This may sound a bit blasé, but a well-faked demo of a totally original 2040 technology is going to be more well received than a well-designed product with 2011 technologies.

This varies depending on the particular group at the lab, of course--some groups, such as Biomechatronics (http://biomech.media.mit.edu/) are more grounded in reality, whereas others, such as Lifelong Kindergarten (http://llk.media.mit.edu/) are more experimental.

My advice: READ THE PAPERS that Media Lab groups are publishing. Especially recent Phd theses, and papers at the high-profile conferences (SIGGRAPH, SIGCHI). Think about them. Write about them. Figure out how you'd build upon them. Then talk to the authors of the ones that excite you the most.

NOTE: This is based upon my own experience, and my views do not represent those of the Media Lab. I've worked at the Media Lab in the past, but I'm not speaking from any official capacity here.