recent update caused Outlook 2003’s junk mail filter to stop working. While you could uninstall updates, try Detect and Repair first. It many cases it will fix the problem. Restarting Outlook or rebooting the computer may also fix problems caused by updates.

In fact, any time something stops working as expected try Detect and Repair or Office Diagnostics (Outlook 2007) first. You’ll find them on the Help menu.