On windows I used BitComet torrent client which has great feature - download files in preview mode so I can see movies right away.
uTorrent declared to be able to download files in preview mode but in real it doesn't.
Which torrent client has real preview mode?
qBittorrent
qBittorrent developers claim to be producing a "free" alternative to uTorrent.
One of their features is Sequential downloading (aka "Download in order")
However, this feature is with a health warning:
First install qBittorrent from the software center.
Download the torrent using qBittorrent and right click and select "Download in sequential order".
Utorrent is actually ok to view preview if setting are set correct. But like bakytn said kTorrent has this feature, but you have to look at the files you download to be sure if it works.(Like an .avi file should be no problem) But i dont know when it comes to .rar files that are splittet up e.g.
Try kTorrent.. or qTorrent maybe also i think..
And if it is sequential downloading you can turn that on or off or set the priority higher on some files e.g in the most torrent clients that i have used..
Good luck! :)
last versions of kTorrent 100% support preview. However it requries KDE libs