While perhaps not as robust as merlyn's method, there's a much simpler way to do it. Just turn on autoflush ($| = 1) and have your script start outputting to the browser right away. Then update your progress bar every so often while your script runs. Here's a simple example:

#!perl -w
use strict;
use CGI;

$| = 1; # turn on autoflush

print CGI->header;
print "Progress: ";

for (1..10) {
  print '.';
  sleep 2;
}

print "\n<br><br>Done!";
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