dannybuoy:Basically, yes you ned a password. You should have a built in account named Administrator and this should have a password. You would have been prompted to enter the password when installing the OS but if you didn't install it yourself you might not know it. You can either use this Administrator account (so you can leave your main account password-less as it is) or add a password to your personal one.
Additionally, you have to supply the username in the format .\Administrator or .\Bill. (The dot inidicates the user belongs to the local machine.)
If you add a password to your own account though, you might want to configure auto-logon so you don't have to type in the password every time you turn the PC on:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
AutoAdminLogon = "1"
DefaultUserName = "Bill"
DefaultPassword = "password"
Please note that in Vista's Default install, the Administrator account is disabled, so unless you enable this account, you can't just use the administrator account. If you want to enable it (not really recommended), let me know and I'll post instructions.
I personally use the autologin mentioned above (though that is the first time I've seen that method).