If I recall, Outlook 2000 in Internet Mode Only creates only a single mail
profile across all users and not one specific to each user.  Use regedit to
examine the key
HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\WIndows
Messaging Subsystem and look what's underneath it.  There should be a
Profiles key with one more key below that that mentions the Internet

If you don't need IMAP account access, if you reconfigure OL 2000 to
Corporate/Workgroup mode, you should be able to have separate mail profiles
for each user.

As to the missing data, by creating the account for the second user, you've
changed the common profile to point to the other person's PST, which the
first person can't access.  The first person's PST is probably still in his
or her Windows profile.  Its default location is the hidden folder
%UserName%\Local Settings\Application Data\Microsoft\Outlook.