Microsoft just announced two or three updates are required before you install window vista SP1.The updates are required are depend on the edition of window vista.Prereqiusite update 935509 is apply for window vista enterprise and ultrimate only.
1.Update 933509 – for window vista enterprise and ultrimate only,ensure bitlocker drive encryption normal operation.
2.Update 938371 – update several internal components for install and unistall window vista SP1 purpose.
3.Update 937287 – for software and language pack,optional window features installation and removal .
To obtain the 933509 update,click ‘START’ ->’CONTROL PANEL’ ->’SECURITY’ ->’WINDOW UPDATE’ ->’CHECK FOR UPDATES’
More information,please visit Microsoft support center.