Are you using WinXP Pro or what? If so, the default way to get into the Administrator account is to boot up in safe mode. Once logged in, you can change the way the logon works so that you can get to the Adminstrator account at any time. To do this, you disable the welcome screen. And, for security, you force CTRL+ALT+DEL to bring up a login screen where you can type the username and password for the account you want to login to.
To disable the "Welcome Screen" interactive logon. That's the logon screen that lists all the users, you click a button and up pops the place to type the password, if there is one. Go into control panel and users, then user accounts. Go into "Change the way users log on or off". Uncheck both the "Use fast user switching" and the "Use Welcome screen", then click OK. Close all of the screens.
To force CTRL+ALT+DEL, go to Administrator Tools in the control panel and then double click Local Security Policy. In local security on the left click Local Policies, which expands the item. Under there you'll see Security Options. Highlight that one on the left (click once). On the right, scroll down to find "Interactive Logon: Do not require CTRL+ALT+DEL". Double click that and then choose the "disable" radio button. Click OK and close all active windows.
Now, reboot. You should then be presented with a little white box that says "Press CTR+ALT+DEL to log in". Do so. Afterwards, you should see a standard white box window asking for the username and password. This is where you can type any user name, but specifically the word "Administrator" for the username and then the Administrator's password. Note, the password may be blank, so just pressing OK may log you in.
Once you can get into the Administrator account, you can finish setting up your domain.
