Microsoft Provides a tool name "Qfecheck.exe", which is used for enumerating installed hot-fixes on a system. However this tool can work only for Windows 2000 and XP.
The complete article and tutorial can be found online here
http://support.microsoft.com/kb/282784
For later Operating System (2003, Vista, 7 , 2008) ; you can use this WMI command
"wmic qfe".
