Outlook Express

Do you have a large number of messages in any of the default Outlook Express folders?  If so, that may be one cause.  Microsoft recommends either creating your own folders from within OE, or storing large quantities of mail outside the application.  (From experience, I recommend option #2.) 

You might also try running the Internet Explorer/OE Repair function from Add-Remove Programs in Control Panel.  Just double click the entry for Internet Explorer 5.5 and Accessories, and follow the prompts to Repair instead of Remove Internet Explorer.  Reboot when prompted, amd see if things work any better.  You'll want to be connected to the internet when you run the Repair tool, as it may be necessary to download replacement files.

http://support.microsoft.com/default.aspx?scid=kb;en-us;194177&Product=ie550

In that case, you may want to try the fixes suggested here:

http://support.microsoft.com/default.aspx?scid=kb;en-us;235300&Product=oex