As far as I know, you will need to use AppleScript Studio or a third party utility to accomplish this. X-Commands, soon to be released and renamed to Extra Suites, offers a progress bar, as does 24U Appearance OSAX.
VERY old thread, I know, found it looking for a possibilty to make a status bar, got this idea, don’t know how it would work though, haven’t tested it in a process…:
display dialog "approx 5 minutes left" giving up after 60
display dialog "approx 4 minutes left" giving up after 60
display dialog "approx 3 minutes left" giving up after 60
display dialog "approx 2 minutes left" giving up after 60
display dialog "approx 1 minute left" giving up after 60