By Default Vista created a "Limited" account when you install it. You do not get the Admin account by default. They do this to try and help prevent issues.
Remember that cute "Administrator" account you see when you login to safe mode? That's the built-in administrator account that's installed by default, and disabled by default too, after a little digging-in I made this tutorial that'll let you enable and use this account in normal mode, and with a little other tweak, enjoying an XP-like administrator experience, while UAC is left ON (or off, it doesn't matter), but with no prompts or right clicks.
For Windows Vista Ultimate/Business/Enterprise:
1- Click Start, and type "secpol.msc" in the search area and click Enter. (You may receive a prompt from UAC, approve/login and proceed)
2- In the left list, choose "Local Policies", then "Security Options"
3- Set "Accounts: Administrator account status" to Enabled.
4- Set "User Account Control: Admin Approval Mode for the Built-in Administrator account" to Disabled.
For Windows Vista Home Basic/Home Premium:
1- Click Start, and type "cmd" in the search area, right click on "Command Prompt" and select 'Run as Administrator".
2- In the command prompt type "net users Administrator /active'" (Note the capital "A" in Administrator) and press Enter, you will get a confirmation as "The command completed successfully".
3- Click Start, and type "regedit" in the search area and click Enter, navigate to: [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\Curr entVersion\Policies\System]
Double click on "FilterAdministratorToken" and set it to "0"
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Now log-off, and you'll see new account named "Administrator" is available, click on it to login.
Now you are the master of your domain! I recommend if you're going to use this method is to apply it as soon as you do a fresh install of Windows, so you can simply delete whatever administrator you've created in the setup process, and make this one the "real" administrator for your PC, also you can rename this new admin account or change its password like any other account from "User Accounts" in the Control Panel.
A last note: Please apply this procedures only if you know what you're doing. Disabling security features in the operating system is not something recommended to the average Joe, and for sure I won't be held accountable for any damaging happens to your system or files resulting from running a full administrator account all the time.
From Tantawi @ Neowin
That will get you the Admin account upon log in.