Some helpful tips....
Well some Imagineers do float around these forums but its not likely you'll hear anything back. When Imagineers are asked how did you become an Imagineer each person will tell you a different story. My suggestion is this:
Either become a cast member, beef up your portfolio with ideas and make some contacts (like the person said above).
Or you could wait till you are a Jr. or Sr. in college and enter the WDI's Imagi-Nations University Design Contest (if it's still going on then). This is another way to get noticed. The contest is amazing and is open to only certain majors so you may wanna check it out. In the mean time if you're not close to any of the parks to become a CM you can always study hard, design your heart out and research. There are sooooooo many great books out there that deal with WDI. These can help alot. I, myself am a Sr. in college majoring in Fine Art with the hopes of becoming an Imagineer oneday. It's hard to make fine art professors and advisors understand what Imagineering is and what you can do if you become one. There are certain colleges that do however know what WDI is and have alot of connections. The best being CalArts. Alas I didn't go there, wish now I would of but things happen for a reason. I have spent the last 2 years conviencing my University's Fine Art department that WDI is something special. I am known on campus as the "Disney Kid."
Alot of people ask what should I study to become an Imagineer? Well the answer there is just as wide. I e-mailed WDI back in 98 and asked and they shot me a long list of classes that I should consider and I thought... there goes that dream I would be in college for years. I stuck with art and entered the WDI Imagi-Nations contest and placed well. Once that happened I got the bug and have been designing attractions, shows, and hotels for my portfolio and working on Disney inspired art for my portfolio and senior show.
Point being is there is no way one can tell you how to become an Imagineer you just have to have the dream and passion for it. Good luck in all you do.