Vista - Keyboard problems Office 2007

I have a DELL desktop and keyboard (USB port) running WindowsXP and Office 2007
When working in any of the Office programs (Outlook, Excel or Word) the
keyboard will suddenly start producing different keystrokes as if we have
moved all the keys around and changed the layout. The timing is random but
not the layout. It's the same (wierd) layout each time (e.g. ;=s, ,=z
etc). If I'm in Word when it happens, typing in Excel or Outlook is fine and
vise versa. To reset, I close the affected program and start it again. Then
it's fine until the next time. Happened 3 times this morning. It's not a
'Language' issue, and I've swapped out the keyboard. Can anyone help?
Thanks,
--
Ian W
South Africa