Normally XP Home and Vista Home have user account management tools with limited functionality, so user have to use console tools to create/manage groups. XP Home User manager can manage user and group accounts on Microsoft Windows XP, Vista and Windows 7 Home editions. Also, User Manager supports privileges assignment. For example, you can allow regular users to change system time.
Short list of features:
user account management (password, password expiry, disable/enable, account expiry, home dir, profile path)
local group management
privileges management (grant and revoke privileges to users and groups)