Installshield conditions

The condition for a first time install is:
Not Installed

For a complete uninstall:
REMOVE~="ALL"

For any maintenance operation (repair, modify, uninstall, anything except first time install):
Installed


The above came in handy when I ended up wrting this to not display a messagebox on a silent install:

function WarnUserIfNotSilent(hMSI)
  STRING szProperty;
  NUMBER iSize;
begin  
  iSize = 256;
  if (MsiGetProperty (ISMSI_HANDLE, "UILevel", szProperty, iSize) = ERROR_SUCCESS) then
    if (StrCompare(szProperty, "2") != 0) then
      MessageBox("A message.", WARNING);    
    endif;
  endif;
end;