Cant open MS Outlook

I tried to change my server from that of my former empoyer to my personal
Yahoo - and now am getting error message " the file c:\doc and
settings\E\local\app\data\ms\outlook1.ost cannot be accessed. You must
conect to your MS Exchange Server Computer at least once before you can use
your offline folder file".

I have my Microsoft Office Basic Edition 2003 disc - and could reload it -
but I dont want to lose info from the program that is installed.

Sure would 'preciate some help. If you like, I will phone you.