I have read a few so-called definitive guides on Windows XP file and printer sharing; honestly none of them were even in the same zip code as definitive. I have always been concerned about the importance and the role of Simple File Sharing in Windows XP networks. You can find this setting in:
Control Panel → Folder Options → View tab → Advanced Settings list → Use simple file sharing (Recommended) checkbox at the bottom of the list
Today, Microsoft Support article 304040 helped me realize the massive impact of this setting on Windows networks. In summary, this configuration alters the way Windows authenticates and authorizes network users. I recommend all Windows XP users to review this article as soon as possible.
Confidential Files! 