Hi Adam,
When you install ArcPad 10, it will detect which version of ArcMap you have installed on your machine.
If it is ArcMap 9.3, then you will have an ArcPad 10 installation, BUT the ArcPad Data Manager Toolbar (in ArcMap) will be the ArcPad 8 Toolbar.
If it is ArcPad 10, then you will have and ArcPad 10 installation and the ArcPad Data Manager Toolbar will be the ArcPad 10 Toolbar (new features and functionality).
So either way - your version of ArcPad will be ArcPad 10 -it is only the ArcMap Tools that will be different depending on your version of ArcMap.
If you are planning on upgrading your ArcMap installation from 9.3 to 10, you will need to uninstall and reinstall ArcPad to detect the new version and install the new tools.
Thanks,
Hannah 🙂