You might not see the security tab for a file or folder when using an XP client for the following reasons:
You do not have enough permissions to see the security settings of the file or folder
Simplified file sharing is enabled on your client
To disable simplified file sharing, choose Control Panel→Folder Options→View, and deselect Use Simple File Sharing (Recommended), and click Apply.
For more information about disabling simplified file sharing and setting permissions on a shared folder, see Microsoft knowledge base article 307874.