The Google Talk gateway works just like the other IM gateways for the most part. Here are two special things to watch out for.
One Google Talk gateway per queue. With the other IM gateways, you can have more than one gateway on a given protocol (such as AIM) on any given queue. With Google Talk, only one Google Talk gateway per queue will work. If you need more than one Google Talk gateway in your overall service, create separate queues for them and assign the desired operators (you can assign the same group of operators to more than one queue).
Google Talk for Google Apps users. If you use Google Apps, you need to use your full address as the Google Talk username. The gateway will take care of the rest. Example: email@example.com