Wirelessly posted (BB 8900: BlackBerry8900/4.6.1.250 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/301)
Tiger or leopard? Pop3 or imap? Have yo enabled settings in your gmail account?
The basic gist of it is this:
Pick pop3 (non-synchronizing) or imap (synchronizing)
Enable pop3 or imap in gmail settings
Mail should automatically detect server settings, so just set the name, pw, and pop/imap