As was said in the other thread by Merlyn:
This works under modern Apache, but under older Apache versions, the script
also had to be named nph-something to turn off the buffering. Consider the name
as a signal that Apache should do its own $| = 1 equivalent.

I don't know why it doesnt work under 2.0 apache, but try renaming the script "nph-..." and looking into the docs on CGI.pm. That is how you get around apache's buffering.