I voted 5, but even that might be tough. As well as it has done, this could be a banner year for movies at least in terms of box office and the number surpassing $200M. The Matrix still has another movie coming in November, and as much as some were disappointed in #2, they will be back to see how it ends. The Lord of the Rings ends the trilogy in December. There's no way that won't be number 1 for movies starting this year, though I guess if you only count box office receipts from 2003, it might be tough to pass $250 million in only 12 days (releases 12/19 I think).
So I am guessing that Nemo will fall just short of catching Matrix 2 which will put it at #2 for those released so far. LoTR and Matrix 3 I think will both surpass it as well, which makes it 4th. If any of the big summer movies (T3, Hulk, Pirates) do well, they will also pass $270M which is about where Nemo will end up, I am guessing. If there's a big surprise hit, that could push it back to 6th. Candidates for that later in the year are Cat in the Hat and Last Samurai.
One thing that I must say surprises me is how well Nemo has done. As much as I liked it, in my opinion it is not as good as any of the other Pixar movies, even falling short of Bug's Life for me. Monsters Inc and Toy Story (both) are just such great movies, hard to pass them. I think the lack of an original great song is a problem for it for me, though I did find myself singing Beyond the Sea for several days! Also, it was GREAT to see an animated movie actually feature a father. It's been quite a while since that happened! I am sure I am forgetting some movie, but it seems like all of them feature some sort of broken home, most often with a missing, dead or inexplicably absent father.