Windows Vista sidebar was completely independent of user account control. However in windows 7 sidebar with gadget and UAC are related means if you turn of or disable UAC in windows 7 then sidebar will not work.This has been done to prevent users from installing any malicious unsigned desktop gadget in windows 7. Since most of the users prefer to keep User Account control (UAC) disabled, they wont be able to enjoy desktop gadgets and sidebar in windows 7, well here is small work around basically a registry hack to make windows 7 sidebar with gadget to work when UAC is disabled or turned off.
Check It: Run Windows Sidebar Gadgets With UAC Disabled In Windows 7