A member of this forum (stinsondog) has compiled a great web page dedicated to this. See it here: http://home.comcast.net/~tamsterra/OP/Gmail.htm
This will show you how to set up gmail to forward to your BB which is a better setup then the regular setup as it is instant. I use it and it is great.
Be sure to thank him (stinsondog) if (when) it is helpful.