Hi Greg,
I doubt it's anything to do with an update. I could understand pressing Tab when you're in overtype mode deleting the selection, but that shouldn't happen in insert mode.
Try the approaches suggested here (there's a fair bit of overlap):
http://support.microsoft.com/kb/921541
http://word.mvps.org/FAQs/AppErrors/...artingWord.htm and
http://lounge.windowssecrets.com/ind...owtopic=197827
for various series of troubleshooting steps that will help you track down (and hopefully solve) the problem.