> Why can't the PIC run from the 3V supply too ?

IMHO 3V is just too low for that circuit. If the high- and low-side
drivers each drop a volt (the 2003 at least has Darlington outputs),
after the current-limiting resistor that leaves crumbs for the LEDs.
And the LEDs are an important part of this project

At such a low voltage for a row-column switching arrangement I'd
be experimenting with more suitable components. N-ch FETs or
transistors with low saturation, such as Zetex NPN, on the low-side
and P-ch FETs or Zetex PNP on the high-side

Either that or bump up Vcc to at least 5V. The PIC Vcc can be
limited within that

Cost is a consideration of course, but if it doesn't work properly
it doesn't matter how cheap it is

I would not be happy with this as a "last minute" circuit. There are
so many things that need to be worked out IMHO it's nowhere near
ready

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