Vista (x86) and projectors

I need to use a projector as well as my monitor to display slideshows. I'm
using an nVidia 7600GT graphics card. With my old system (with a Matrox Dual
Head G550 card) all I had to do was turn on the dual head mode and use it as
a clone of the main monitor. No problem, when I turned off the projector the
system was fine displaying on just the main monitor and when shut down and
powered on later it booted fine.

If I set up the nVidia card to run in a similar fashion and plug in the
projector everything works fine (after a lot of fiddling with resolutions
etc) - and if I turn off the projector, everything continues to work fine,
until I turn off the system and reboot. Once it gets to the part of loading
Vista, the monitor goes blank and immediately goes into 'Power Save' Mode.
Vista continues to load, it's just that I cannot see anything on the monitor.

If I switch back to just using the one monitor in the nVidia control panel,
then everything works as normal.

If I forget to revert to a single monitor and if I turn on the projector,
then Vista will load and the monitor acts normally. Obviously I don't want
to have to turn the projector on every time I boot the system or switch back
to a single monitor in the nVidia control panel.

Anybody with any ideas??

Thanks