How can i add a custom paper size?

Hi! I am using AutoCAD 2012 and I'm trying to create a custom paper size, but I am not being sucessfull. The printer is a HP Deskjet 1220c. I added the custom paper size in the Windows printer server, but the created paper size don't show up in AutoCAD. Also, the option in AutoCAD to add a custom paper size is disabled. How can I proceed?

PS: sorry for my bad English, I'm not a native speaker.