i used to be able to do that with my nivida card in my laptop, then i build a PC and the nvidia software didn't include that feature. try going on your video card's website and see if they got any add on drivers or programs.
Either way, Preferably one taskbar across two monitors (eventually 3). Also I am running Windows 7. I love the ability to "Pin" programs to the taskbar and would like to be able to do the same for the taskbars on other monitors.
Also, I cant believe MS didnt include that feature out of the box.
You can set diaplays up to be in groups I believe, not sure how it is done in windows as I have always done this through the ATI or Nvidia drivers. An extended desktop is just free space, if you group monitors at the same resolution it will make one LARGE desktop and the taskbar will span across all of them.
Actual Multiple Monitors will solve all your problems. It support Pin, Jump lists, Aero ... , and etc on all secondary taskbars. Moreover, It grant you start button, show desktop button, notification area on secondary taskbars..
Read this article http://actualtools.com/articles/detail.php?ID=1265