Disney Imagineering RARELY (if ever) hires straight out of college. They prefer people with practical experience in their field, and an education to back it up.
My suggestion would be, study art and engineering, attempt to get a job in the entertainment industry (not as a performer necessarily, but rather, as a designer), or in the amusement industry (non-disney end of it, also as a designer), or get a job with Disney doing something else...
THEN aim for imagineering.
Also... Joe Rohde, head of WDI for AK, put it best.
"There aren't any classes you can take to be an imagineer. It's more of an aptitude."
So.. just have fun and don't burn yourself out trying to become an imagineer.