Try
Taskbar & System Tray > TaskBand > Basic > TaskBand > TaskItemButton
Taskbar & System Tray > TaskBand > Basic > TaskBand > UncombinedTaskItemLeft
Taskbar & System Tray > TaskBand > Basic > TaskBand > UncombinedTaskItemCenter
Taskbar & System Tray > TaskBand > Basic > TaskBand > UncombinedTaskItemRight
for vertical
Taskbar & System Tray > TaskBand > Basic > TaskBand (Vertical) > TaskItemButton
Taskbar & System Tray > TaskBand > Basic > TaskBand (Vertical) > UncombinedTaskItemLeft
Taskbar & System Tray > TaskBand > Basic > TaskBand (Vertical) > UncombinedTaskItemCenter
Taskbar & System Tray > TaskBand > Basic > TaskBand (Vertical) > UncombinedTaskItemRight
there are 10 images for each Normal, Hover, Pressed, etc.
Jerrt