Then you're using VersaMail, the 'built-in' one.
As I'm not sure which part of the setup you have problems with, this is the URL from GMail that lists the setting
http://mail.google.com/support/bin/a...y?answer=13287 . Pay special attention to the ports as GMail uses its own.
Also, don't forget to enable "POP" in GMail as illustrated here:
http://mail.google.com/support/bin/a...y?answer=13273 . GMail's POP is not enabled by default.
Hope it helps.