Word 2007 freezes in Vista

I have a brand new Lenovo X61 tablet PC with Vista Business and MS Office
Professional Plus 2007. While working in Word, the system occasionally
freezes, i.e., screen dims and, although I can move the cursor around,
nothing on the computer functions (including CtrlEscDel). I have to use the
power button (press for 5 seconds or so) to reboot. I think (but am not
certain) that this occurs during automatic backup in Word. I haven't noted
problems in Excel or PowerPoint, but I've only been on the system for a week
(and this is my first experience with Vista). Is this a known problem or is
there a fix?