Obviously this is not the best way to have things "networked". Is there a better way to do it over a wireless network since my house is not wired for ethernet?
If your printer is plugged into your router* via ethernet then you shouldn't have to use printer sharing on any of your computers. They should all be able to use it independently as a network printer.
I'm guessing you installed your Z3100 as a network printer on the first computer, then set it to share the printer. Then, on your wireless computer you installed the Z3100 by browsing to the other computer's shared printer. Is that correct? If it is, reinstalling the printer on the wireless system as a network printer should keep the paper size inconsistency from being an issue.
--Drew
*Or anywhere else on your network where it can get its own address, rather than being tied to a single computer.