If you're in the field and only have access to your Juno I don't think there is much you can do. From what I know if you create a new map or quick project it will default to WGS84.
If you have ArcPad installed on a PC, you can choose a different map projection when you create a quick project, it should let you choose something other than the default WGS84. Just navigate to the projection folder and choose GDA94 MGA55; the path should be ArcGIS\ArcPad10.0\Coordinate System\Projected Coordinate Systems\National Grids\Australia. Also, if your working from ArcMap, just export your map using the ArcPad tool and the projection will be maintained.
Fyi, if all you're after are the grid coordinates you can show them even if your map projection is in WGS84. If you tap the status panel and go to the data page, you can change the coordinates displayed by tapping on them and choosing UTM.
Danik