What I have noticed because I have downloaded the game several times the last days cause of firmware flashes is this.

When you go to the Ovi store using the browser on the N900 and click download it seems that nothing happens, but in fact it downloads in the background just not displaying any progress. So when I and probably others click download again and again, the browsers download queue adds up downloads, it all goes slower and finally you get a out of space prompt because many folks don't have the browser cache set to Auto. The largest cache size before auto is 40MB and that's what get full. Set your browser cache to Auto, then try to download the game, then in your browser click on the top menu and select Downloads to see whats going on.