Video size / length of Nikon D5100?

This is very beginner's question, i'm asking this before buying my first DSLR. I just like to know what is the video size for Nikon D5100 in both 720px, 1080px videos.
i heard that it's 4GB for 10min. Is that true?

The maximum for a single clip is either 4gb or about 10 minutes. Exact filesize depends on the scene, the amount of motion but also colours and highlights. Judging from the samples here: http://www.dpreview.com/...page18.asp you're looking at about 2.5mb per second on full hd 30fps.

And to your next question, you'd need an SD card class 6 or better to shoot video, brand isn't that important.