If you have done a clean install of Ubuntu you should see a green icon on the top right, left to the area where the volume and network icons are. Basically its telling you that the nvidia drivers arent opensource, but once you click there you have the activate button and then it will ask your password and then it will download the driver and install it by itself.
I noticed what you said about the password... and I dont really remember if the password can be retrieved by any other means, at worst... start the installation again.
The thing is that with nvidia... you dont really need to download drivers, just activate them and the system does it for you. After the install, however, the system will ask you for a restart.
There are also HOW-TOs on other ways to install drivers, but I would really recommend using the one that they provide there.
If I can be of help... let me know, but keep in mind that I'm not a linux veteran I'm just 2 years into this.