x11 not properly set

[Pol]

With my recently installed opensuse 11.1 on my hp tc4200 tablet. (laptop),
X11 is not working well: sometimes windows disappear for few seconds and 
other minor weird things happen.
My graphics card is intel  915GM

Inspecting the /var/log/Xorg.0.org, i have found three lines with the error
message

  (EE) intel(0): underrun on pipe B!

What is its meaning?
Moreover:

  usbDetect: can not ioctl version
   Wacom xf86WcmWrite error : Input/output error


Any hints?

Thank you
---pol