How can I -

Put all the data entry for account details in one page -
Stop the entry of invalid data field by field as opposed to when the whole form is sent - couldn't the fields within the form be verified to NOT be empty?

Can the shipping details and payment method exist in one page? Is that possible without pulling apart the whole design of the pages?

I am getting feedback that the multiple pages makes it all too hard to get to the payment area and people just give up. Has anyone done any of the above?

Just need some ideas/advice

Joe