The PC going into "sleep" mode or being switched off cannot possibly turn off the router. Provided the router remains powered on at the mains switch, what you do with any computers connected to it is immaterial.
>>> Are you aware of a "Vista bug" which means a
>>> wireless connection is dropped when the PC
>>> sleeps regardless of the user's preference
That is a totally separate issue from the router remaining connected to the exchange over an ADSL enabled phone line, which is what you are trying to do to establish the appropriate "sync" speed.