Plugins? Do you have any programs that have plugins tying into office? If so, try disabling/uninstalling them.
Otherwise, are you sure that it isn't a hardware issue showing up b/c of the Office apps? If the Office apps are the most resource-intensive applications you run, that they are causing just enough stress on your system to where Windows is killing the tasks - just a thought for now, anyway.
(This part I'm going off what the head security guy at our company [it's a really big job where I work] once told me in an off-the-cuff discussion when Vista had been out not terribly long. Basically, Vista somehow handled programs in such a way that they did NOT use the same memory space for the same application/instance every time - which was supposed to be better for security - never took much time to really verify this, though seems I have read it in at least one or two online publications).
Also, with Windows XP and prior, applications generally used the same memory locations. So if it's one application that's causing the issues, it could just be you've got a RAM stick that has one bad section of RAM on it, that nothing else (noticeable) seems to touch.
Have a look at Windows Event Logs:
Start Menu, Right-click 'My Computer', Manage, Event Messages, System (on Vista and 7, you'd specify Windows, THEN System)..