Yeah - during the Windows installation routine, you would have been asked for an Administrator password. Like Dave says, if you don't remember providing one, it's probably blank.
If by any chance that doesn't work, and you had a 'old fogy moment'
when installing Windows, and can't remember what password you put in, you can do the following to quickly reset the password to blank (assuming of course that the user account you use normally is a computer administrator, which I presume it is)
Go to command prompt (Start - Run -
cmd) and then type
net user administrator "" [Enter]
It should say "The command completed successfully.", and then the Administrator password will now be blank
Similarly you can type
net user administrator "newpassword" and it will set it to whatever you type. Note that the quotes aren't strictly necessary, but they are when blanking the password and putting in a password that contains spaces.
Hope this helps