The problem is that even if the videocard supports rotation, the video driver may not. For instance with the ATI video chipsets the proprietary "fglrx" driver doesn't support rotation (that may have changed with the new version released the last couple days) while the Xorg driver "radeon" supports rotation.
Then if the chipset and driver supports rotation you still may have to modify the xorg.conf to get it. For instance nVidia (and maybe Intel) require the line:
to get rotation. It's placed in the:
Option "RandRRotation" "on"
xorg.conf section. I think other cards may require a different but similar RandR option.
Identifier "Configured Video Device"
So what you're asking turns out to require some in depth knowledge. Which Toshiba tablet pc do you have? Maybe knowing that could give us a handle to figure things out.