Resolution required for top-range printed image

Back in February I posted the querie - "I will shortly be going to
Kolkata to collect images for a book I am writing. I have previously
used my Cannon PowerShot A540 with OK
results. ..... Without going overboard how much should I expect
to spend? Thanks!" I received many great replies. Thanks to everyone.
I ended-up buying a Cannon A640. That plus my old Nikon SLR (regular
print film) resulted in many great shots. If I can find out how to do
it I'll post a link to my Picassa Gallery.
Thanks again!
GoFlatty