I found the answer to the problem on experts-exchange.
Open Outlook from the command line and add the /safe option.
Actually, it suggested that I first do the /cleanprofile option. I did that, but it didn't seem to fix it. But maybe doing both like I did makes a difference...
Before I loaded up XP on this computer, all was well with Outlook. I'm connected to an Exchange Server and using Outlook XP. Now, if someone sends me an email, it doesn't show up immediately in my inbox like it used to. New emails only seem to show up when I do something that would otherwise refresh Outlook - like changing to tasks (I'll see new emails suddenly come into my inbox), changing views, or deleting an email.
Sorry if this has been posted before - its hard to come up with a search string to uniquely describe this problem.