automatic name and password

on a new p4 with ie6 i have automatic name and password-entry. i will just have to click ok. how 1.can i get rid of this. pc is for a customer.
2. how can i activate this on a second pc with ie55? name is already automatic but not pass. yahoo sometimes asks name too. i still could not solve this last problem. 3. how can i completely delete all name-possibilities coming, some are wrong.