USER TIME OUT AND CANT GET TO THE EXCHAN

I HAVE HAD 4 USER NOT BE ABLE TO FIND THIE EXCHANGE SERVER IN OUTLOOK 2000 UNDER WINDOWS 98 SE. I AM RUNNING 1 NOVELL SERVER AND 1 NT BOX FOR EXCHANGE. CLIENTS LOG INTO BOTH. 4 USERS HAVE JUST STOPPED BEING ALBE TO LOGG INT TO THERE MAILBOX. BUT THEY CAN BROWSE AND SEE THE NT SERVER IN EXPLORER ADN ACCESS FILES THERE.
I HAVE, DELETED ALL PROFILE INFO AND RECREATED IT, DELETE THEIER NT LOGIN AND CORRESPONDING EMAIL BOX, USED CLEAN MAILBOX, REMOVED NETWORK SETTINGS AND REINSTLLED THEM. 2 ARE DELL P2 AND 2 ARE HP P2S. IM BEGIULED PLEASE HELP, I AM LOW ON TECH POINTS AND ONLY WILL HAVE 48 AFTER POSTING THIS QUESTION.