Outlook 2003 won't open

I just downloaded the trial version of Office 2003. I had already been using
Outlook 2002 on an exchange server. When I try to open outlook 2003 I get
the message:
cannot start microsoft office outlook. unable to open the outlook window.
the set of folders could not be opened.
I've read some of the other posts from people who had similar problems but
I'm not sure what to do. I've found the folder with the .pst file in it.
There are two of them: archive.pst (with today's date) and an older one
called Outlookimap.ku.edu....pst (I used to use an imap server before I
migrated to the exchange server if that is what this file is).
Do I need to do something with these .pst files (do I need the older one?)