In addtion to Brian Fluet's comments you'll need to
enable IMAP access via GMails web interface.

Login to Gmail go to Settings > Forwarding and POP/IMAP
Enable IMAP
Auto-Expunge off
Move the message to the Trash
Do not limit the number of messages in an IMAP folder

Also at GMail - Settings > Labels
Select/deselect which folder you desire to Show in IMAP

I'm having trouble finding concise instructions on how to set up pmail with gmail imap.  I've followed the instructions from 

 http://email.about.com/od/pegasusmailtips/qt/et_access_gmail.htm

 This seems to allow me to send email -- but I can't get anything from the gmail inbox to appear in pmail.

Thanks!! 

An IMAP connection adds a folder to your folder list so make sure you are looking there for the Gmail mailbox.

If that's not it, here are the settings that are working for me.

Connection tab:

     IMAP server address:  imap.gmail.com

     Server port:  993

     Login name and password are your gmail credentials

Settings tab:

     This server supports folders within folders (I don't think this is required)

Performance tab:

     List only subscribed folders in the mailbox

Security tab:

     Via direct SSL connnect