implementing bars in the meantime on of long work

[Giovanni Masullo <giovanni masullo icn siemens it>]

i would like to know the rite "theorical" way to implement a
long job without losing the possibility of get user input.
have i to create a secondary task to do the job, with the primary
waiting for user input?
is there a better way?
and what if i want to implement a completion bar?
there's anybody can help me?
tanx in advance.