I’ve tried a few searches for the warning information provided but came up empty. Could you describe in better detail what you were doing when these warnings were generated, and provide some info on your version of Exchange? Have you noticed any problems with user mailboxes, send/receive functionality, public folders etc. that may be associated with these? The more detail you can provide the better chance your going to have to get a solution.
As for upgrading to Exchange 2003…. well, you can give it a shot, if there are any critical issues with your current version the install will most likely stop and prompt you to correct the problems.