I installed the PECL uploadprogress PHP extension on my Debian Lenny development server for the Drupal filefield module just before Psynaptic's excellent roundup of how it install it on just about everything. But it turns out to be a lot easier on the Ubuntu 9.04 (Jaunty) development server I'm switching too:
sudo pecl install uploadprogress
Then add the "extension=uploadprogress.so" to your php.ini, in my case I'm using a local ini file rather than modifying the apt supplied php.ini:
Reload the Apache config and you're done.