The other night my computer was down and my wife installed ubuntu 7.10 she says it didn't ask for user name or passwords. Is there any way to find out the user name and password?

How do I? That's a crappy thread title. In the future why don't you think of better ones that actually describe your question and thread your starting. Thanks.

And as for your question, just set a new password if you want one. Unless you can decrypt the hash in the /etc/shadow file, you won't know the password. And it's probably logged you in as root.

cat /etc/passwd for a list of system users, root and any others that might be around. Check /etc/shadow to see if they have a password.

PS. I'm changing your title for you since you can't, take my advice in the future, make better titles or get slapped around by members and moderators on this forum.

thats the problem I cant log in except with live cd

Ah then your wife does have the password or she couldn't have finished installing it. Beat it out of her or you can do the simple thing and boot into single user mode and reset the password that way. If it asks for a password, you can pass this on the grub command line during bootup:

init=/bin/bash

Take you right to a shell, just mount /proc and /, then run the passwd command to reset root's password.

she says she dosnt remember it or putting one in. And how do i run in single user mode?

At grub boot prompt in command or edit mode, type: linux single