Outlook Express gone after…

Hello,
I just installed Microsoft Project on a associates workstation. Apparently now that Microsoft Project 2000 is installed, he cannot access Outlook Express. It asked me when I was installing Microsoft Project 2000 if I would like to upgrade IE to 5.0 and I clicked on yes. Now he cannot access his Outlook Express. Does anyone know why? Is his Inbox still located on the drive somewhere? If so, under what sub-directory would it be located under?