PR 1.2 was just released for N9 and one of the biggest features it brought was support for video calling. Google Talk is one of the built in IM clients that support this feature, however it could be the case that after installing PR 1.2 you still weren’t able to see any option to make a video call. For it to work you need to install a Gtalk with video package from the OVI Store. It’s from Nokia directly so it’s about as official as it can get. You can get it here. Make sure you have PR 1.2 installed!
Get Google Talk with video call support on your N9