I have the same setup, plus the Fantasea Bigeye lens and Inon S2000 strobe. I haven't had a chance to dive it yet, but am headed to Maui the end of July.
There are a couple things I would recommend:
In Setup, set the zoom limit to the 5x optical zoom range
Set you image storage mode to raw+jpeg
Beyond that, you might want to put the camera in the housing and use it around the house for several days until you are comfortable with the controls before you dive it.
The WP-DC28 housing does not allow access to the control dial, but you can access virtually all of it's functions using the shortcut and arrow buttons.
There are some good informational posts on the various modes & settings of the G10 on this and other forums, especially the canon forum on scubaboard.com.
Have fun with your new toy!
Tim