-->Windows Xp (sp2), which has generally the same security 
features in windows vista, for example the firewall, 
although windows vista's firewall is now able to monitor 
both inbound and outbound traffic. 
-->Windows Vista has Parental control Feature Windows XP 
has No Parental control Feature "This option enables 
parents to restrict Children’s which sites, games software 
to use".
-->Vista requires more space to install and graphics 
appears to be more beautiful. 

-->BitLocker Drive Encryption is a data protection feature 
available in Windows Vista Enterprise and Ultimate for 
client computers and in Windows Server 2008.

Also there is difference in presence of boot.ini file which is present in XP but not in Vista.
Its one of the major deployment differences.