I'm not sure I understand the question. If you're getting a menu to add a user, you should be able to follow that.
An easy way to set up a user account is via the useradd command. For example, at the shell prompt, type:
Then, again at the shell, type:
This will set up your password.
In order to get to the shell at a new installation, interrupt grub when it boots up. For FC3, you have 3 seconds to do this, by typing the letter "e" (for edit) when grub first prints out the kernel name it is about to boot.
Then, when you get to the next menu, type "e" again. What you want to do is edit the line with the "rhgb quiet"; take out those words and replace them with the word "single". Then boot up. You'll get to single-user mode, and a shell prompt.