The only way to turn off the touchpad is by using Dell's touchpad driver (it's actually programmed by Alps,Synaptics etc....)There are also some software solutions (touchpal,touchfreeze..)but they only temporarily disable the touchpad
If the devicemanager only comes up with a generic Windows driver you won't be able to use added functionality given by Dell's driver.
I recently upgraded to Windows 8 and I knew that the Dell(Alps) driver was not supported - and Win8 wouldn't even let me install it.This didn't bother me at all because I was happy with the generic driver and I had no need to disable the touchpad.
Just recently Alps released a new Windows 8 driver for some inspirons - my inspiron wasn't included - nevertheless some user reported that it would work fine even on the 1545.
So I downloaded the driver, installed it and it worked perfectly.
What I want to say is: if the touchpad hasn't developed a hardware fault,the proper driver is installed AND the OS (windows Xp,7,8) is not corrupted the touchpad should be ok.I can only speak for my inspiron 1545 - and this machine has never let me down.
I recorded the Win8 touchpad installation,which is similar for any other OS and run the utility.You may want to watch it.