1) the client usually provide the English (source language) subtitles in Word file or only provide the movie with/without source language subtitles?
Several possibilities here:
a) They may provide the script in word - too often it doesn't match the final edition - and the film.
b) They might give you the film on DVD, VHS, or electronic file, and nothing else.
c) They might send you just the subtitles (with or without spotting) to translate - you'll never see the film
2) the work includes subtitles translation and putting the translated subtitles onto the movie?
Three successive operations here:
b) Spotting - marking the timecode "in" and "out" for each subtitle,
c) Creating an overlay subtitles "video" file (so the user may turn subtitles on/off while watching), or burning subtitles on the video, which will render a DVD or video file like a subtitled VHS.
3) does this job need a subtitling software? which software is recommended for English to Chinese subtitling?
Only if you intend to do steps (b) and (c) on the previous answer. All I know about Chinese involves food. An excellent freeware starter for subtitling that may get you professional-looking results is Subtitle Workshop, downloadable from http://www.urusoft.net .
4) what's the rate for English to Chinese? usually pay per minutes?
You'll be amazed at the range of rates for subtitling work. AFAIK most pay per minute of total playing time, but there are some that pay per subtitle.
If you need any kind of technical information about video, search in http://www.videohelp.com . Chances are you will find whatever you are looking for.