UPDATED : http://tuto-wave.com/google-wave/how-to-add-google-wave-to-wordpress
To do that you need to have access to Google Wave.
First install the plugin for WordPress wavr. You can got it here.
Install it ( upload, activate).
This plugin need a wave ID to work. Well how we get that ?
First go in your google Wave.
Google Wave
Look at the top menu menu.
Google Wave Top Menu
You see the menu Debug ? Here you can find a lot of options for your wave. A lot of them are obscur for me. But See the “Get Current Wave ID” Item ?
Google Wave Debug Menu
Click on it ! Yeah !
wave id
Now go in WordPress. Create a New post. Put a title, You can write some text. To start the wave write
[toto id="XXXXXX"]
Replace toto by wave. I didn’t write wave to not start a wave 
.
The quote ” ” around the id code are optional.
And that’s it. You can do every thing in Google Wave know.
You can also take a look in the plugin option to configure some visual options.
Well, for the moment nobody will able to see and answer. But it is fun 
! Me I wait for my invitation !