Q: Have just deleted daughters guest visitor log in. Have my pass word. Don't remember my user ID now on start up screen.

Hmmmm,not sure if this helps with forgtten username, but maybe!???

Reset Password 10.7, 10.8...

http://reviews.cnet.com/8301-13727_7-20087723-263/how-to-run-the-password-reset- utility-in-os-x-10.7-lion/

Then Reset your Keychain...

http://support.apple.com/kb/TS1544

If not, I think this still works in 10.8.x, but maybe not if it's a Firmware PW set...

Reset OS X Password Without an OS X CD...

http://theappleblog.com/2008/06/22/reset-os-x-password-without-an-os-x-cd/

Admin Hack...

http://www.hackmac.org/?q=node/4

Starts up like the first time you buy a new Mac, but after filling in all that info again, you should have access to the computer and the other Users & files will still be there... give the new User a different name than an existing one.