php could do this with flush and sleep used together. here is some code that works to output something, wait a second and then output more.
<?php
<?php
echo "<!--";
for ($j = 0; $j < 255; $j++) {
echo "z";
}
echo "-->\n";
flush();
for ($i = 0; $i < 5; $i++) {
echo "$i<br />\n";
flush();
sleep(1);
}
?>
test it here
p.s. i forgot to mention internet explorer (sucks) wont display ouput until it receives 255 bytes of data. so if you want i.e. to properly run this code, you may need to just output 255 bytes of random data before running the flush code and put it in an html <!-- comment --> so it wont show up.