Do you have a problem with Outlook 2002/2003's autocomplete cache not working, but 'Suggest names while completing to To, CC, BCC fields' is enabled in Tools, Options, Preferences, E-mail Options, Advanced?

Try renaming the *.NK2 file for your profile (C:\Documents and Settings\USERNAME\Application Data\Microsoft\Outlook) and restart Outlook. Outlook will create a new one for you.

Notes:
You can rename or delete the NK2 file if you want to get rid of all addresses in your autocomplete file.

Outlook 2000/98 doesn't offer autocomplete, only autoresolution. Autoresolution information is stored in a file with the extension 'nick'. You can delete it to reset your autoresolution data.