http://www.slipstick.com/outlook/olcat.htm
Master Category List The master category list is not a separate file, but instead is part of the Windows Registry. Each user has a different category list
To back up the Master Category List in Outlook 97/98:
Run Regedit and go to HKEY_CURRENT_USERSoftwareMicrosoftOffice8.0Outlook and select the Categories key.
Choose Registry | Export Registry File to make a copy of the Categories branch of the registry.
To back up the Master Category List in Outlook 2000:
Run Regedit and go to HKEY_CURRENT_USERSoftwareMicrosoftOffice9.0Outlook and select the Categories key.
Choose Registry | Export Registry File to make a copy of the Categories branch of the registry.
To back up the Master Category List in Outlook 2002:
Run Regedit and go to HKEY_CURRENT_USERSoftwareMicrosoftOffice10.0Outlook and select the Categories key.
Choose Registry | Export Registry File to make a copy of the Categories branch of the registry.
You can use this exported branch to distribute a category list to other Outlook users. See the MSKB article How to Migrate Custom Categories to Other Users. CAUTION: Using a .reg file to propagate a category list does not update a user’s own list; instead it completely replaces it. I personally do not recommend this method, because it eliminates much the utility of the Category feature for users. See the next section for what I think is a better method.
If you remove a category from the master list, any items marked with that category are not affected. In the Categories dialog box, that category is listed as “(not in master list).”
Also see:
OL2000 Custom Categories Are Not Transferred from Outlook 2000 to Outlook 2002
http://support.microsoft.com/?kbid=303937