Clear your cache to force ObjectDock Plus to load with the defaults. This will tell you whether or not the program is supported to use tabs on the tablet.
Note - 'cache' is a general term for the stored preference/configuration files for the ObjectDock program. These files are kept in a normally hidden folder which is referred to by ChrisH in comment #3.
To clear the cache:
1 - Close ObjectDock
2 - Open "My Computer > Tools menu > Folder Options > View tab" and then select and apply 'Show hidden files and folders'.
3 - Go to "C:\Documents and Settings\USERNAME\Local Settings\Application Data\Stardock" folder (where "C:\" is the hard drive with the user folders) and delete the "ObjectDock Plus" folder found there.
4 - Start ObjectDock which should now load with a tabbed and non-tabbed dock.
That should do it unless there is something missing in the installation or OS support.