RegWriteDWordValue

function RegWriteDWordValue(const RootKey: Integer; const SubKeyName, ValueName: String; const Data: Cardinal): Boolean;

Writes the specified REG_DWORD-type registry value. Returns True if successful, False otherwise.

begin
  RegWriteDWordValue(HKEY_CURRENT_USER, 'Software\My Company\My Program',
    'ShowToolbar', 1);
end;