My company uses Outlook for email/calendars but I'm a big Google Apps user and was wondering if it's possible to implement Google Apps for my company so there can be a choice if someone wants to use Google's apps or Outlook.
It is possible to setup a split delivery scenario where email traffic is sent to primary email system. You users are split on different email systems, for example Exchange and Google Apps. If the primary email system have the user, it will send the email to the secondary email system for delivery. This is a very common scenario in Google Apps enterprise setup.
It's also possible to setup dual delivery where emails are delivered to two email systems at once. A scenario suited for backup or transformation from one system to another.
I've seen GMail used as a client for an Exchange server through POP3. You simply need to enable the Microsoft Exchange POP3 service on the Exchange server. This will not sync your calendar, though.
I know many companies that use Google Apps as their platform and Outlook as the client. If your company is using Exchange Server, then the change will be less likely to occur. If your Outlook is connect to an ISP e-mail via POP3 or IMAP, then changing to Google Apps will be very easy to do.