Trying to setup my outlook 2007 with gmail but I keep on getting error messages?

My company has recently purchased some accounts from gmail for our emails, and when I tried to set up my outlook 2007 to work with my gmail so that I can send, receive and open my email through outlook, I keep on getting an error about my imap and a box appears every second from time to time asking me to enter my username and password and don’t know why I may be facing the problem, my coworkers setup thier outlook the same way that I did and didn’t face any of the problems that I am faceing, if you know what might be causing these problems, please help !