Installed Joomla on 10.6 server, everything is working except for uploads...

Hi, I recently installed my first website with joomla on Mac OS X Snow Leopard Server. Everything is ok, joomla is running well except for upload.

Cannot upload anything, I think that I need to set the right permissions for the folders, with the right user (the user that access via browser).

Anyone knows how to make it?

Thanks in advance,