If you preform a complete format of the PC and a reinstall of your operating system and programs, OneCare will only be restoring data files. No program files are ever backed up by OneCare. Therefore, I believe that the corrupt file would not be restored by OneCare as it has not been backed up by OneCare.
However, I would probably not take the advice of the Expression Web tech and I'd suggest heading over to the Expression newsgroups where some very knowledgeable people may be able to offer some ideas for you.
http://www.microsoft.com/communities/newsgroups/list/en-us/default.aspx?dg=microsoft.public.expression.discussion&cat=en_us_67e78a72-5803-4cf7-95dc-24991e9f5a00&lang=en&cr=us
If they can't help directly, they can steer you in the right direction and perhaps save you from the complete format.
-steve