Epcot will be 25 in 2007, I believe it opened in October of 1982. The only reason I remember this is because we stayed at the Poly on our honeymoon and we took the monorail over to Epcot and saw it all before it was open from above. I believe we had to pay for it if I remember correctly. We were thrilled to return home and tell everyone we saw the "Big Ball" !
I also think the Magic Kingdom was celebrating its 10th Birthday during that trip so perhaps they will have a Big Birthday Part, MK 35 years and Epcot's Silver Anniversary.