XP-Tabs have been deprecated for a long time now, but you can still use them by setting the tab type to xp-Tab, instead of Tab.
However this is not recommended. Better to use the new styles throughout the application, including the tabs. That way you can set the app to look the way you want, based on the overall style.
You _may_ need to turn on support for the XP-Tabs script on the WebServer Scripts tab (I don't recall exactly.)
Please note that this feature may be removed in the future.
cheers
Bruce