Ok, I literally just did this myself.
First, make sure you have enabled IMAP in Gmail.
Second, through your Storm's Browser goto:
BlackBerry Internet Service
Third, go here and follow these steps through your Storm's Browser:
https://mail.google.com/support/bin/...y?answer=78882 Start at #5
*I had to delete my email address from the BIS site and start over because it was originally setup for POP.
** After some initial tests, reading/deleting emails on my Storm does so in my Gmail account. Conversely, reading/deleting emails in my Gmail account have yet to update on my Storm.
*** When sending emails from my Storm, I no longer receive the sent email as a new message on my Storm but it does show up on my Gmail account in the Sent box AND the Inbox (As a delivery confirmation; wait nevermind about that confirmation. Forgot to change setting on my Storm)