Like torin3 mentioned, the command needs to be run w/ Administrative privileges (Right click the Command Prompt shortcut in the Start menu, and select "Run as Administrator). In addition, you may need to replace the - in the command... bcdedit.exe -set loadoptions DDISABLE_INTEGRITY_CHECKS w/ a forward slash:
bcdedit.exe /set loadoptions DDISABLE_INTEGRITY_CHECKS
... or as linked to above, you could try disabling it via the Group Policy Editor: Start | Run | Type gpedit.msc, and click OK | Expand the following branch...
User Configuration | Administrative Templates | System | Driver Installation
In the RH pane right click the "Code signing for drivers" setting--> Properties | Under the "Setting" tab select the "Ignore" radio button. And like jrafael mentioned above, VistaBootPro can accomplish the same thing by editing the Boot Configuration Data (BCD) store.