What is involved in networking an XP desktop computer with a VISTA Laptop?

You do not have to have the same username and pword, in fact that is a bad idea. Less secure. Run through the wizard as you already did on one machine. Then go to the other machine and run that wizard for networking. Just enter the correct info. Do you have a router or switch/hub? Or are you trying to connect them to each other? need more information to help further.