Until now, only iPhone and iPod touch users could sync their contacts with Address Book in Mac OS X 10.5. Starting with Mac OS X 10.6, syncing Gmail contacts is also available to users who don’t have an iPhone or iPod touch. If your Mac is running Snow Leopard, you can turn on contact sync in the Address Book preferences. The syncing is better, too: in Mac OS X 10.6, only contacts in Gmail's "My Contacts" group’re synced, rather than all of Gmail's contact suggestions. And photos’re now transferred as well, since sometimes you just need to put a face to a name.
For some reason my Address Book prefs don't include the lower portion contained in your screenshot, namely Synchronize contacts with MobileMe, Exchange, Yahoo, or Google. Strange.
Ahhh, just found it under the account. Your screenshots must be from a pre-released version of Snow Leopard.
Yes, the screenshot was of previous version. I couldn't locate update image at the time of posting.