the few times I've called kinko's, they've told me to set it at 300 dpi. hence it's likely a 300 dpi poster (18X24 inches) done at kinko's will be nearly as good to the untrained eye as a 3000 dpi poster, but it will be 100 times faster to transmit, load and print. they use hp printers AFAIK - available to the consumer.