As opposed to the first closed beta, which was merely a self extracting exe, the second version now is packed in the regular installer again you should be used to from the last versions of Fleet Operations. The beta version now - without any soundtracks - is 200mb big. The final version should be about the same size, so you know what you can expect if you have a slower internet connection. Compared to the file size of some current game demos, 200mb is of course nothing that is worth to be mentioned at all. Installed, 3.0 takes up about 1gb space on your hdd.

Donators can download the second beta version from the 3.0 beta forum.
As the readme/changelog is as good as final, all changelog lovers can get it here
3.0 Readme download