Where downloaded files is located?
It stored in /var/mobile/Library/Downloads by default. You can change this location on "Save To" tab: click on '..' to go upper level, then on folder name. IF THIS FOLDER DOES NOT EXIST OR READ ONLY, YOU WILL STUCK IN 0% PROGRESS FOREVER. IN THIS CASE, SET SAVE TO /tmp OR OTHER DIR WRITABLE BY SAFARI
How to open downloaded file?
You need to use the separate application. For a movies, I recommend VLC or yxflash player from the cydia. You also can use ifile
How to delete downloaded file?
Swipe on file name in "Save To" tab, then tap "Delete"
Which firmware versions is supported?
It created on 3.2.x and never touched any more. Looks like version 5 is still works
What is .itorrent or .fastresume dir?
This directory contain various temporary files. You can delete it safetely after torrent is downloaded.
How to jailbreak?
Please check this