Outlook has a Rules Wizard that will work with a POP3 Internet account as well as an Exchange client account. It filters my messages in Outlook XP/2002 with my POP3 accounts, I don't use an Exchange account for that. If you do have an Exchange account, the Rules are stored on an Exchange server and follow around your Exchange profile.
Not sure what "Inbox Assistant" is, maybe a Wizard, or an older version of the "Rules Wizard" for older Outlook versions?