Lol!
I'm not sure, but if u think that it took a year to make and release the 1st movie, and the same for the second, and its taking 18 months for the third, then if the time scale follows then we should probably see GoF late 2006!! i mean if you think about all the things that they have to build for GoF, such as the world cup quidditch stadium, all the things for the trials etc. And just the general content of it, i can see it taking AGES to make unfortunately.
Its a shame cause it would be great if we could have a HP movie released every xmas, along with a LoTR's movie too!