>I don't think you would be able to do a precize prediction, because too many external factors are involved. However, you may try to gather some statistics, by measuring speed of copying different files in different time of the day with various PC load at the moment. Then you can use an average time, which may be only 10% close to the truth in each particular case...

And I don't really need any prediction - I just need to show "50% done" when it's really done. Since I'm showing the times of each such line, the prediction is left to the user :).