IMHO the throws would be difficult to practice safely if you have no experience. If you insist on practicing throws - practice FALLING A LOT first. Also, both should wear a Judogi (or heavy jacket) that each can hold onto to control the fall.
However, some of the grappling side of Judo could be more possible to learn without an instructor. I would not recommend practicing joint locks or chokes without an instructor - permanent damage or death can occur if you aren't careful. However, hold downs should be fine. Note that Brazilian Ju-Jitsu would probably offer more grappling options, but the Judo grappling is still pretty good. http://www.judoinfo.com/