Select the HP Designjet Z3100 from the list of printers.  There may be more than one so check the IP address as well.

Click the Color Center Tab to get a set of options that you can synchronize with our computer.

Select Manage Papers.

Select Update Paper list.  This will install all of the paper sizes and types of the Z3100 on your computer.  That way when you  do Page Setup you can select the same paper size that the printer supports.