Hmm, I don't know what msimn.exe is. I use Outlook, not Outlook Express, so I guess that's the correct exe. Question for you: does Internet Explorer ever crash on you? Do you use Windows Messenger or MSN Messenger by any chance? If not, try going into the Outlook Express preferences and disable the option to "Enable Instant Messaging with Microsoft Outlook Express" or something of that sort. I have had problems with that in the past making Outlook hang.
You say you just reformatted your computer. Did this start happening right from the start? Were you able to set up your mailbox (email address, pop3/smtp server, etc) without it hanging?
It seems like it might be some software or drivers that you re-installed after you reformatted. After you reformatted, did you try out Outlook Express first thing before installing anything else? Did it work then? After what did you install when it stopped working?
Also, if you have an Nvidia video card, you have Nvidia drivers installed. You can always go to the www.nvidia.com website and download the latest drivers (sometimes this fixes freezing issues.) If you don't do this, Microsoft installs stripped down (and old) versions of the drivers itself.