The administrative share is for corporate use, primarily, to allow network administrators to access the system. Windows XP is based off of the Windows NT code base, which historically was a corporate operating system. However, rest assured that for anyone to be able to connect to that share, which will be re-created on each reboot after you remove it, they would need to know your username and password.
If you want to disable it permanently, I think the answer you are looking for is documented here.
