As you have likely found, the Aux fan can be activated under the engine/DDE module (in the activate menu) but you need to make sure you have selected the correct DDE variant (or you might get the script errors you are seeing).
I cannot quite remember what the correct module is labeleed in INPA - my '05 uses the DDE5.0 module, so I'm guessing you '06 is the same.
If you think INPA is a bag of monkeys, wait until you try DIS..!!
Actually, I find INPA to be very relaiable, as is DIS (once I got it going that is).