When you use Drupal imagefield or filefield module, you'll have noticed that it uses uploadprogress to show a nifty progress bar. This is optional but it's a nice thing to have and it's actually not that difficult to install. Just follow this article: http://smbjorklund.no/how-enable-pecl-uploadprogress-extention-mamp
Here is the extension that has been precomplied so you can just simply drop it into your folder and activate it. The zip file contains uploadprogress.so and zip.so (so you can use zip extension files).
Unzip the file and place both *.so file into directory: /MAMP/bin/php5/lib/extensions/no-debug-non-zts-20060613/
Then add this line:
to your php.ini file which can be found at /MAMP/Config/php5/
Make sure you restart your web server.