This command will set the variable to true if Vista / Win 7 UAC ( User Account Control ) is enabled.
System,HasUAC,<%var%>
This is necessary, since UAC can cause problems while building some projects.
System,HasUAC,%var% If,%var%,Equal,True,begin Message,"Error: UAC is enabled. This may cause problems when building.",INFORMATION,15 Halt,"Error: UAC is anabled. This may cause problems when building. " End