mmmpffmmppffm i'll try to explain this one.

The PLLDIV factor is the one you need to reduce the external OSC to 4MHZ. Yes the internal OSC will always work @4MHZ and raise it to 96MHZ... later

In your cas 12MHZ external /4MHZ internal = PLLDIV should be 3.. you have it good

USBDIV/2 will be the PIC OSC SPEED. in this case 48MHZ.

P.D. Is the word "requiered" well written?
i could be wrong... but i think it's 'required' or 'needed'

Francais un jour, francais toujours