Might depend on whether the XPPro is 32bit or 64bit, not sure. I believe it behaves the same on 32bit as it does on XPHome.
On XPHome you have to be logged on as an administrative user, or start ObjectDock using the right-click "run as" option and use an admin user name and password while logged in as a limited user. While using the "run as" option the ltd user is actually using the admin's ObjectDock themes and can overwite one of the admin's themes if saved with the same theme name.
Also, while logged in as a limited user, you can use the "run as" with the admin logon/passwerd once each time after the ltd user logs in to get the services started, then "Unload Object Dock", and then restart it again normally and the systray should then load, and you will no longer be sharing object dock themes between the users. The "run as" admin has to be executed once each time after the ltd user logs in to start the systray services though.