Outlook98 not running under user profile

I’ve got several Win2Kpro workstations and am beating my head against a wall with this problem. My users can’t open Outlook98 unless I make them part of the power users group on their local workstations. I don’t want them to be able to install software, so this is a problem. We aren’t connecting to an Exchange server, just using Outlook to do internet mail with an SMPT/POP3 server. Anyone have any ideas?